Merge tag 'hyperv-fixes-signed-20260607' of git://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux

Pull hyperv fixes from Wei Liu:

 - MSHV driver fixes from various people (Anirudh Rayabharam, Can Peng,
   Dexuan Cui, Michael Kelley, Jork Loeser, Wei Liu)

 - Hyper-V user space tools fixes (Thorsten Blum)

 - Allow VMBus to be unloaded after frame buffer is flushed (Michael
   Kelley)

* tag 'hyperv-fixes-signed-20260607' of git://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux:
  mshv: support 1G hugepages by passing them as 2M-aligned chunks
  Drivers: hv: vmbus: Improve the logic of reserving fb_mmio on Gen2 VMs
  mshv: use kmalloc_array in mshv_root_scheduler_init
  mshv: Add conditional VMBus dependency
  hyperv: Clean up and fix the guest ID comment in hvgdk.h
  drm/hyperv: During panic do VMBus unload after frame buffer is flushed
  Drivers: hv: vmbus: Provide option to skip VMBus unload on panic
  mshv: unmap debugfs stats pages on kexec
  mshv: clean up SynIC state on kexec for L1VH
  mshv: limit SynIC management to MSHV-owned resources
  hv: utils: replace deprecated strcpy with strscpy in kvp_register
  hv: utils: handle and propagate errors in kvp_register
  mshv: add a missing padding field

15 files changed, 206 insertions, 111 deletions

diff --git a/drivers/gpu/drm/hyperv/hyperv_drm_drv.c b/drivers/gpu/drm/hyperv/hyperv_drm_drv.c
index 06b5d96e6eaf..b6bf6412ae34 100644
--- a/drivers/gpu/drm/hyperv/hyperv_drm_drv.c
+++ b/drivers/gpu/drm/hyperv/hyperv_drm_drv.c
@@ -150,6 +150,10 @@ static int hyperv_vmbus_probe(struct hv_device *hdev,
 		goto err_free_mmio;
 	}
 
+	/* If DRM panic path is stubbed out VMBus code must do the unload */
+	if (IS_ENABLED(CONFIG_DRM_PANIC))
+		vmbus_set_skip_unload(true);
+
 	drm_client_setup(dev, NULL);
 
 	return 0;
@@ -169,6 +173,7 @@ static void hyperv_vmbus_remove(struct hv_device *hdev)
 	struct drm_device *dev = hv_get_drvdata(hdev);
 	struct hyperv_drm_device *hv = to_hv(dev);
 
+	vmbus_set_skip_unload(false);
 	drm_dev_unplug(dev);
 	drm_atomic_helper_shutdown(dev);
 	vmbus_close(hdev->channel);
diff --git a/drivers/gpu/drm/hyperv/hyperv_drm_modeset.c b/drivers/gpu/drm/hyperv/hyperv_drm_modeset.c
index 7978f8c8108c..d48ca6c23b7c 100644
--- a/drivers/gpu/drm/hyperv/hyperv_drm_modeset.c
+++ b/drivers/gpu/drm/hyperv/hyperv_drm_modeset.c
@@ -212,15 +212,16 @@ static void hyperv_plane_panic_flush(struct drm_plane *plane)
 	struct hyperv_drm_device *hv = to_hv(plane->dev);
 	struct drm_rect rect;
 
-	if (!plane->state || !plane->state->fb)
-		return;
+	if (plane->state && plane->state->fb) {
+		rect.x1 = 0;
+		rect.y1 = 0;
+		rect.x2 = plane->state->fb->width;
+		rect.y2 = plane->state->fb->height;
 
-	rect.x1 = 0;
-	rect.y1 = 0;
-	rect.x2 = plane->state->fb->width;
-	rect.y2 = plane->state->fb->height;
+		hyperv_update_dirt(hv->hdev, &rect);
+	}
 
-	hyperv_update_dirt(hv->hdev, &rect);
+	vmbus_initiate_unload(true);
 }
 
 static const struct drm_plane_helper_funcs hyperv_plane_helper_funcs = {
diff --git a/drivers/hv/Kconfig b/drivers/hv/Kconfig
index 2d0b3fcb0ff8..aa11bcefddf2 100644
--- a/drivers/hv/Kconfig
+++ b/drivers/hv/Kconfig
@@ -74,6 +74,7 @@ config MSHV_ROOT
 	# e.g. When withdrawing memory, the hypervisor gives back 4k pages in
 	# no particular order, making it impossible to reassemble larger pages
 	depends on PAGE_SIZE_4KB
+	depends on HYPERV_VMBUS if HYPERV_VMBUS
 	select EVENTFD
 	select VIRT_XFER_TO_GUEST_WORK
 	select HMM_MIRROR
diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 84eb0a6a0b54..89d214dda360 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -952,6 +952,7 @@ void vmbus_initiate_unload(bool crash)
 	else
 		vmbus_wait_for_unload();
 }
+EXPORT_SYMBOL_GPL(vmbus_initiate_unload);
 
 static void vmbus_setup_channel_state(struct vmbus_channel *channel,
 				      struct vmbus_channel_offer_channel *offer)
diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
index ae60fd542292..ef4b1b03395d 100644
--- a/drivers/hv/hv.c
+++ b/drivers/hv/hv.c
@@ -272,6 +272,9 @@ void hv_synic_free(void)
 /*
  * hv_hyp_synic_enable_regs - Initialize the Synthetic Interrupt Controller
  * with the hypervisor.
+ *
+ * Note: When MSHV is present, mshv_synic_cpu_init() intializes further
+ * registers later.
  */
 void hv_hyp_synic_enable_regs(unsigned int cpu)
 {
diff --git a/drivers/hv/hv_kvp.c b/drivers/hv/hv_kvp.c
index 0d73daf745a7..336b278b2182 100644
--- a/drivers/hv/hv_kvp.c
+++ b/drivers/hv/hv_kvp.c
@@ -27,6 +27,7 @@
 #include <linux/connector.h>
 #include <linux/workqueue.h>
 #include <linux/hyperv.h>
+#include <linux/string.h>
 #include <hyperv/hvhdk.h>
 
 #include "hyperv_vmbus.h"
@@ -93,7 +94,7 @@ static void kvp_send_key(struct work_struct *dummy);
 static void kvp_respond_to_host(struct hv_kvp_msg *msg, int error);
 static void kvp_timeout_func(struct work_struct *dummy);
 static void kvp_host_handshake_func(struct work_struct *dummy);
-static void kvp_register(int);
+static int kvp_register(int);
 
 static DECLARE_DELAYED_WORK(kvp_timeout_work, kvp_timeout_func);
 static DECLARE_DELAYED_WORK(kvp_host_handshake_work, kvp_host_handshake_func);
@@ -127,24 +128,23 @@ static void kvp_register_done(void)
 	hv_poll_channel(kvp_transaction.recv_channel, kvp_poll_wrapper);
 }
 
-static void
+static int
 kvp_register(int reg_value)
 {
-
 	struct hv_kvp_msg *kvp_msg;
-	char *version;
+	int ret;
 
 	kvp_msg = kzalloc_obj(*kvp_msg);
+	if (!kvp_msg)
+		return -ENOMEM;
 
-	if (kvp_msg) {
-		version = kvp_msg->body.kvp_register.version;
-		kvp_msg->kvp_hdr.operation = reg_value;
-		strcpy(version, HV_DRV_VERSION);
+	kvp_msg->kvp_hdr.operation = reg_value;
+	strscpy(kvp_msg->body.kvp_register.version, HV_DRV_VERSION);
 
-		hvutil_transport_send(hvt, kvp_msg, sizeof(*kvp_msg),
-				      kvp_register_done);
-		kfree(kvp_msg);
-	}
+	ret = hvutil_transport_send(hvt, kvp_msg, sizeof(*kvp_msg),
+				    kvp_register_done);
+	kfree(kvp_msg);
+	return ret;
 }
 
 static void kvp_timeout_func(struct work_struct *dummy)
@@ -186,9 +186,8 @@ static int kvp_handle_handshake(struct hv_kvp_msg *msg)
 	 */
 	pr_debug("KVP: userspace daemon ver. %d connected\n",
 		 msg->kvp_hdr.operation);
-	kvp_register(dm_reg_value);
 
-	return 0;
+	return kvp_register(dm_reg_value);
 }
 
 
diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
index 05a36854389a..eb8bdd8bb1f5 100644
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h
@@ -441,7 +441,6 @@ void hv_vss_deinit(void);
 int hv_vss_pre_suspend(void);
 int hv_vss_pre_resume(void);
 void hv_vss_onchannelcallback(void *context);
-void vmbus_initiate_unload(bool crash);
 
 static inline void hv_poll_channel(struct vmbus_channel *channel,
 				   void (*cb)(void *))
diff --git a/drivers/hv/mshv_debugfs.c b/drivers/hv/mshv_debugfs.c
index 418b6dc8f3c2..3c3e02237ae9 100644
--- a/drivers/hv/mshv_debugfs.c
+++ b/drivers/hv/mshv_debugfs.c
@@ -674,8 +674,10 @@ int __init mshv_debugfs_init(void)
 
 	mshv_debugfs = debugfs_create_dir("mshv", NULL);
 	if (IS_ERR(mshv_debugfs)) {
+		err = PTR_ERR(mshv_debugfs);
+		mshv_debugfs = NULL;
 		pr_err("%s: failed to create debugfs directory\n", __func__);
-		return PTR_ERR(mshv_debugfs);
+		return err;
 	}
 
 	if (hv_root_partition()) {
@@ -710,6 +712,9 @@ remove_mshv_dir:
 
 void mshv_debugfs_exit(void)
 {
+	if (!mshv_debugfs)
+		return;
+
 	mshv_debugfs_parent_partition_remove();
 
 	if (hv_root_partition()) {
diff --git a/drivers/hv/mshv_regions.c b/drivers/hv/mshv_regions.c
index fdffd4f002f6..6d65e5b42152 100644
--- a/drivers/hv/mshv_regions.c
+++ b/drivers/hv/mshv_regions.c
@@ -29,29 +29,27 @@
  * Uses huge page stride if the backing page is huge and the guest mapping
  * is properly aligned; otherwise falls back to single page stride.
  *
- * Return: Stride in pages, or -EINVAL if page order is unsupported.
+ * Return: Stride in pages.
  */
-static int mshv_chunk_stride(struct page *page,
-			     u64 gfn, u64 page_count)
+static unsigned int mshv_chunk_stride(struct page *page, u64 gfn,
+				      u64 page_count)
 {
-	unsigned int page_order;
+	unsigned int page_order = folio_order(page_folio(page));
 
 	/*
 	 * Use single page stride by default. For huge page stride, the
-	 * page must be compound and point to the head of the compound
-	 * page, and both gfn and page_count must be huge-page aligned.
+	 * folio order must be at least PMD_ORDER, the page's PFN must be
+	 * 2M-aligned (so that a 2M-aligned tail page of a larger folio is
+	 * acceptable), and both gfn and page_count must be 2M-aligned.
 	 */
-	if (!PageCompound(page) || !PageHead(page) ||
+	if (page_order < PMD_ORDER ||
+	    !IS_ALIGNED(page_to_pfn(page), PTRS_PER_PMD) ||
 	    !IS_ALIGNED(gfn, PTRS_PER_PMD) ||
 	    !IS_ALIGNED(page_count, PTRS_PER_PMD))
 		return 1;
 
-	page_order = folio_order(page_folio(page));
-	/* The hypervisor only supports 2M huge page */
-	if (page_order != PMD_ORDER)
-		return -EINVAL;
-
-	return 1 << page_order;
+	/* Use 2M stride always i.e. process 1G folios as 2M chunks */
+	return 1 << PMD_ORDER;
 }
 
 /**
@@ -86,15 +84,14 @@ static long mshv_region_process_chunk(struct mshv_mem_region *region,
 	u64 gfn = region->start_gfn + page_offset;
 	u64 count;
 	struct page *page;
-	int stride, ret;
+	unsigned int stride;
+	int ret;
 
 	page = region->mreg_pages[page_offset];
 	if (!page)
 		return -EINVAL;
 
 	stride = mshv_chunk_stride(page, gfn, page_count);
-	if (stride < 0)
-		return stride;
 
 	/* Start at stride since the first stride is validated */
 	for (count = stride; count < page_count; count += stride) {
diff --git a/drivers/hv/mshv_root_main.c b/drivers/hv/mshv_root_main.c
index bd1359eb58dd..146726cc4e9b 100644
--- a/drivers/hv/mshv_root_main.c
+++ b/drivers/hv/mshv_root_main.c
@@ -2241,7 +2241,7 @@ static int mshv_root_scheduler_init(unsigned int cpu)
 	outputarg = (void **)this_cpu_ptr(root_scheduler_output);
 
 	/* Allocate two consecutive pages. One for input, one for output. */
-	p = kmalloc(2 * HV_HYP_PAGE_SIZE, GFP_KERNEL);
+	p = kmalloc_array(2, HV_HYP_PAGE_SIZE, GFP_KERNEL);
 	if (!p)
 		return -ENOMEM;
 
diff --git a/drivers/hv/mshv_synic.c b/drivers/hv/mshv_synic.c
index e2288a726fec..88170ce6b83f 100644
--- a/drivers/hv/mshv_synic.c
+++ b/drivers/hv/mshv_synic.c
@@ -13,6 +13,7 @@
 #include <linux/interrupt.h>
 #include <linux/io.h>
 #include <linux/cpuhotplug.h>
+#include <linux/hyperv.h>
 #include <linux/reboot.h>
 #include <asm/mshyperv.h>
 #include <linux/acpi.h>
@@ -456,46 +457,75 @@ static int mshv_synic_cpu_init(unsigned int cpu)
 	union hv_synic_siefp siefp;
 	union hv_synic_sirbp sirbp;
 	union hv_synic_sint sint;
-	union hv_synic_scontrol sctrl;
 	struct hv_synic_pages *spages = this_cpu_ptr(synic_pages);
 	struct hv_message_page **msg_page = &spages->hyp_synic_message_page;
 	struct hv_synic_event_flags_page **event_flags_page =
 			&spages->synic_event_flags_page;
 	struct hv_synic_event_ring_page **event_ring_page =
 			&spages->synic_event_ring_page;
+	/*
+	 * VMBus owns SIMP/SIEFP/SCONTROL when it is active.
+	 * See hv_hyp_synic_enable_regs() for that initialization.
+	 */
+	bool vmbus_active = hv_vmbus_exists();
 
-	/* Setup the Synic's message page */
+	/*
+	 * Map the SYNIC message page. When VMBus is not active the
+	 * hypervisor pre-provisions the SIMP GPA but may not set
+	 * simp_enabled — enable it here.
+	 */
 	simp.as_uint64 = hv_get_non_nested_msr(HV_MSR_SIMP);
-	simp.simp_enabled = true;
+	if (!vmbus_active) {
+		simp.simp_enabled = true;
+		hv_set_non_nested_msr(HV_MSR_SIMP, simp.as_uint64);
+	}
 	*msg_page = memremap(simp.base_simp_gpa << HV_HYP_PAGE_SHIFT,
 			     HV_HYP_PAGE_SIZE,
 			     MEMREMAP_WB);
 
 	if (!(*msg_page))
-		return -EFAULT;
-
-	hv_set_non_nested_msr(HV_MSR_SIMP, simp.as_uint64);
+		goto cleanup_simp;
 
-	/* Setup the Synic's event flags page */
+	/*
+	 * Map the event flags page. Same as SIMP: enable when
+	 * VMBus is not active, already enabled by VMBus otherwise.
+	 */
 	siefp.as_uint64 = hv_get_non_nested_msr(HV_MSR_SIEFP);
-	siefp.siefp_enabled = true;
-	*event_flags_page = memremap(siefp.base_siefp_gpa << PAGE_SHIFT,
-				     PAGE_SIZE, MEMREMAP_WB);
+	if (!vmbus_active) {
+		siefp.siefp_enabled = true;
+		hv_set_non_nested_msr(HV_MSR_SIEFP, siefp.as_uint64);
+	}
+	*event_flags_page = memremap(siefp.base_siefp_gpa << HV_HYP_PAGE_SHIFT,
+				     HV_HYP_PAGE_SIZE, MEMREMAP_WB);
 
 	if (!(*event_flags_page))
-		goto cleanup;
-
-	hv_set_non_nested_msr(HV_MSR_SIEFP, siefp.as_uint64);
+		goto cleanup_siefp;
 
 	/* Setup the Synic's event ring page */
 	sirbp.as_uint64 = hv_get_non_nested_msr(HV_MSR_SIRBP);
-	sirbp.sirbp_enabled = true;
-	*event_ring_page = memremap(sirbp.base_sirbp_gpa << PAGE_SHIFT,
-				    PAGE_SIZE, MEMREMAP_WB);
 
-	if (!(*event_ring_page))
-		goto cleanup;
+	if (hv_root_partition()) {
+		*event_ring_page = memremap(sirbp.base_sirbp_gpa << HV_HYP_PAGE_SHIFT,
+					    HV_HYP_PAGE_SIZE, MEMREMAP_WB);
 
+		if (!(*event_ring_page))
+			goto cleanup_siefp;
+	} else {
+		/*
+		 * On L1VH the hypervisor does not provide a SIRBP page.
+		 * Allocate one and program its GPA into the MSR.
+		 */
+		*event_ring_page = (struct hv_synic_event_ring_page *)
+			get_zeroed_page(GFP_KERNEL);
+
+		if (!(*event_ring_page))
+			goto cleanup_siefp;
+
+		sirbp.base_sirbp_gpa = virt_to_phys(*event_ring_page)
+				>> HV_HYP_PAGE_SHIFT;
+	}
+
+	sirbp.sirbp_enabled = true;
 	hv_set_non_nested_msr(HV_MSR_SIRBP, sirbp.as_uint64);
 
 	if (mshv_sint_irq != -1)
@@ -518,28 +548,30 @@ static int mshv_synic_cpu_init(unsigned int cpu)
 	hv_set_non_nested_msr(HV_MSR_SINT0 + HV_SYNIC_DOORBELL_SINT_INDEX,
 			      sint.as_uint64);
 
-	/* Enable global synic bit */
-	sctrl.as_uint64 = hv_get_non_nested_msr(HV_MSR_SCONTROL);
-	sctrl.enable = 1;
-	hv_set_non_nested_msr(HV_MSR_SCONTROL, sctrl.as_uint64);
+	/* When VMBus is active it already enabled SCONTROL. */
+	if (!vmbus_active) {
+		union hv_synic_scontrol sctrl;
+
+		sctrl.as_uint64 = hv_get_non_nested_msr(HV_MSR_SCONTROL);
+		sctrl.enable = 1;
+		hv_set_non_nested_msr(HV_MSR_SCONTROL, sctrl.as_uint64);
+	}
 
 	return 0;
 
-cleanup:
-	if (*event_ring_page) {
-		sirbp.sirbp_enabled = false;
-		hv_set_non_nested_msr(HV_MSR_SIRBP, sirbp.as_uint64);
-		memunmap(*event_ring_page);
-	}
-	if (*event_flags_page) {
+cleanup_siefp:
+	if (*event_flags_page)
+		memunmap(*event_flags_page);
+	if (!vmbus_active) {
 		siefp.siefp_enabled = false;
 		hv_set_non_nested_msr(HV_MSR_SIEFP, siefp.as_uint64);
-		memunmap(*event_flags_page);
 	}
-	if (*msg_page) {
+cleanup_simp:
+	if (*msg_page)
+		memunmap(*msg_page);
+	if (!vmbus_active) {
 		simp.simp_enabled = false;
 		hv_set_non_nested_msr(HV_MSR_SIMP, simp.as_uint64);
-		memunmap(*msg_page);
 	}
 
 	return -EFAULT;
@@ -548,16 +580,15 @@ cleanup:
 static int mshv_synic_cpu_exit(unsigned int cpu)
 {
 	union hv_synic_sint sint;
-	union hv_synic_simp simp;
-	union hv_synic_siefp siefp;
 	union hv_synic_sirbp sirbp;
-	union hv_synic_scontrol sctrl;
 	struct hv_synic_pages *spages = this_cpu_ptr(synic_pages);
 	struct hv_message_page **msg_page = &spages->hyp_synic_message_page;
 	struct hv_synic_event_flags_page **event_flags_page =
 		&spages->synic_event_flags_page;
 	struct hv_synic_event_ring_page **event_ring_page =
 		&spages->synic_event_ring_page;
+	/* VMBus owns SIMP/SIEFP/SCONTROL when it is active */
+	bool vmbus_active = hv_vmbus_exists();
 
 	/* Disable the interrupt */
 	sint.as_uint64 = hv_get_non_nested_msr(HV_MSR_SINT0 + HV_SYNIC_INTERCEPTION_SINT_INDEX);
@@ -574,28 +605,47 @@ static int mshv_synic_cpu_exit(unsigned int cpu)
 	if (mshv_sint_irq != -1)
 		disable_percpu_irq(mshv_sint_irq);
 
-	/* Disable Synic's event ring page */
+	/* Disable SYNIC event ring page owned by MSHV */
 	sirbp.as_uint64 = hv_get_non_nested_msr(HV_MSR_SIRBP);
 	sirbp.sirbp_enabled = false;
-	hv_set_non_nested_msr(HV_MSR_SIRBP, sirbp.as_uint64);
-	memunmap(*event_ring_page);
 
-	/* Disable Synic's event flags page */
-	siefp.as_uint64 = hv_get_non_nested_msr(HV_MSR_SIEFP);
-	siefp.siefp_enabled = false;
-	hv_set_non_nested_msr(HV_MSR_SIEFP, siefp.as_uint64);
+	if (hv_root_partition()) {
+		hv_set_non_nested_msr(HV_MSR_SIRBP, sirbp.as_uint64);
+		memunmap(*event_ring_page);
+	} else {
+		sirbp.base_sirbp_gpa = 0;
+		hv_set_non_nested_msr(HV_MSR_SIRBP, sirbp.as_uint64);
+		free_page((unsigned long)*event_ring_page);
+	}
+
+	/*
+	 * Release our mappings of the message and event flags pages.
+	 * When VMBus is not active, we enabled SIMP/SIEFP — disable
+	 * them. Otherwise VMBus owns the MSRs — leave them.
+	 */
 	memunmap(*event_flags_page);
+	if (!vmbus_active) {
+		union hv_synic_simp simp;
+		union hv_synic_siefp siefp;
 
-	/* Disable Synic's message page */
-	simp.as_uint64 = hv_get_non_nested_msr(HV_MSR_SIMP);
-	simp.simp_enabled = false;
-	hv_set_non_nested_msr(HV_MSR_SIMP, simp.as_uint64);
+		siefp.as_uint64 = hv_get_non_nested_msr(HV_MSR_SIEFP);
+		siefp.siefp_enabled = false;
+		hv_set_non_nested_msr(HV_MSR_SIEFP, siefp.as_uint64);
+
+		simp.as_uint64 = hv_get_non_nested_msr(HV_MSR_SIMP);
+		simp.simp_enabled = false;
+		hv_set_non_nested_msr(HV_MSR_SIMP, simp.as_uint64);
+	}
 	memunmap(*msg_page);
 
-	/* Disable global synic bit */
-	sctrl.as_uint64 = hv_get_non_nested_msr(HV_MSR_SCONTROL);
-	sctrl.enable = 0;
-	hv_set_non_nested_msr(HV_MSR_SCONTROL, sctrl.as_uint64);
+	/* When VMBus is active it owns SCONTROL — leave it. */
+	if (!vmbus_active) {
+		union hv_synic_scontrol sctrl;
+
+		sctrl.as_uint64 = hv_get_non_nested_msr(HV_MSR_SCONTROL);
+		sctrl.enable = 0;
+		hv_set_non_nested_msr(HV_MSR_SCONTROL, sctrl.as_uint64);
+	}
 
 	return 0;
 }
@@ -673,9 +723,7 @@ mshv_unregister_doorbell(u64 partition_id, int doorbell_portid)
 static int mshv_synic_reboot_notify(struct notifier_block *nb,
 			      unsigned long code, void *unused)
 {
-	if (!hv_root_partition())
-		return 0;
-
+	mshv_debugfs_exit();
 	cpuhp_remove_state(synic_cpuhp_online);
 	return 0;
 }
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index d28ff45d4cfd..b80a35c778ab 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -69,19 +69,29 @@ bool vmbus_is_confidential(void)
 }
 EXPORT_SYMBOL_GPL(vmbus_is_confidential);
 
+static bool skip_vmbus_unload;
+
+/*
+ * Allow a VMBus framebuffer driver to specify that in the case of a panic,
+ * it will do the VMbus unload operation once it has flushed any dirty
+ * portions of the framebuffer to the Hyper-V host.
+ */
+void vmbus_set_skip_unload(bool skip)
+{
+	skip_vmbus_unload = skip;
+}
+EXPORT_SYMBOL_GPL(vmbus_set_skip_unload);
+
 /*
  * The panic notifier below is responsible solely for unloading the
  * vmbus connection, which is necessary in a panic event.
- *
- * Notice an intrincate relation of this notifier with Hyper-V
- * framebuffer panic notifier exists - we need vmbus connection alive
- * there in order to succeed, so we need to order both with each other
- * [see hvfb_on_panic()] - this is done using notifiers' priorities.
  */
 static int hv_panic_vmbus_unload(struct notifier_block *nb, unsigned long val,
 			      void *args)
 {
-	vmbus_initiate_unload(true);
+	if (!skip_vmbus_unload)
+		vmbus_initiate_unload(true);
+
 	return NOTIFY_DONE;
 }
 static struct notifier_block hyperv_panic_vmbus_unload_block = {
@@ -2317,8 +2327,8 @@ static acpi_status vmbus_walk_resources(struct acpi_resource *res, void *ctx)
 		return AE_NO_MEMORY;
 
 	/* If this range overlaps the virtual TPM, truncate it. */
-	if (end > VTPM_BASE_ADDRESS && start < VTPM_BASE_ADDRESS)
-		end = VTPM_BASE_ADDRESS;
+	if (end >= VTPM_BASE_ADDRESS && start < VTPM_BASE_ADDRESS)
+		end = VTPM_BASE_ADDRESS - 1;
 
 	new_res->name = "hyperv mmio";
 	new_res->flags = IORESOURCE_MEM;
@@ -2385,6 +2395,7 @@ static void vmbus_mmio_remove(void)
 static void __maybe_unused vmbus_reserve_fb(void)
 {
 	resource_size_t start = 0, size;
+	resource_size_t low_mmio_base;
 	struct pci_dev *pdev;
 
 	if (efi_enabled(EFI_BOOT)) {
@@ -2392,6 +2403,24 @@ static void __maybe_unused vmbus_reserve_fb(void)
 		if (IS_ENABLED(CONFIG_SYSFB)) {
 			start = sysfb_primary_display.screen.lfb_base;
 			size = max_t(__u32, sysfb_primary_display.screen.lfb_size, 0x800000);
+
+			low_mmio_base = hyperv_mmio->start;
+			if (!low_mmio_base || upper_32_bits(low_mmio_base) ||
+			    (start && start < low_mmio_base)) {
+				pr_warn("Unexpected low mmio base %pa\n", &low_mmio_base);
+			} else {
+				/*
+				 * If the kdump/kexec or CVM kernel's lfb_base
+				 * is 0, fall back to the low mmio base.
+				 */
+				if (!start)
+					start = low_mmio_base;
+				/*
+				 * Reserve half of the space below 4GB for high
+				 * resolutions, but cap the reservation to 128MB.
+				 */
+				size = min((SZ_4G - start) / 2, SZ_128M);
+			}
 		}
 	} else {
 		/* Gen1 VM: get FB base from PCI */
@@ -2412,8 +2441,10 @@ static void __maybe_unused vmbus_reserve_fb(void)
 		pci_dev_put(pdev);
 	}
 
-	if (!start)
+	if (!start) {
+		pr_warn("Unexpected framebuffer mmio base of zero\n");
 		return;
+	}
 
 	/*
 	 * Make a claim for the frame buffer in the resource tree under the
@@ -2423,6 +2454,8 @@ static void __maybe_unused vmbus_reserve_fb(void)
 	 */
 	for (; !fb_mmio && (size >= 0x100000); size >>= 1)
 		fb_mmio = __request_region(hyperv_mmio, start, size, fb_mmio_name, 0);
+
+	pr_info("hv_mmio=%pR,%pR fb=%pR\n", hyperv_mmio, hyperv_mmio->sibling, fb_mmio);
 }
 
 /**
@@ -2897,7 +2930,8 @@ static void hv_crash_handler(struct pt_regs *regs)
 {
 	int cpu;
 
-	vmbus_initiate_unload(true);
+	if (!skip_vmbus_unload)
+		vmbus_initiate_unload(true);
 	/*
 	 * In crash handler we can't schedule synic cleanup for all CPUs,
 	 * doing the cleanup for current CPU only. This should be sufficient
diff --git a/include/hyperv/hvgdk.h b/include/hyperv/hvgdk.h
index 384c3f3ff4a5..f538144280ca 100644
--- a/include/hyperv/hvgdk.h
+++ b/include/hyperv/hvgdk.h
@@ -10,18 +10,12 @@
 
 /*
  * The guest OS needs to register the guest ID with the hypervisor.
- * The guest ID is a 64 bit entity and the structure of this ID is
+ * The guest ID is a 64-bit entity and the structure of this ID is
  * specified in the Hyper-V TLFS specification.
  *
- * While the current guideline does not specify how Linux guest ID(s)
- * need to be generated, our plan is to publish the guidelines for
- * Linux and other guest operating systems that currently are hosted
- * on Hyper-V. The implementation here conforms to this yet
- * unpublished guidelines.
- *
  * Bit(s)
  * 63 - Indicates if the OS is Open Source or not; 1 is Open Source
- * 62:56 - Os Type; Linux is 0x100
+ * 62:56 - OS Type; Linux is 0x1
  * 55:48 - Distro specific identification
  * 47:16 - Linux kernel version number
  * 15:0  - Distro specific identification
diff --git a/include/hyperv/hvhdk.h b/include/hyperv/hvhdk.h
index 5e83d3714966..0c89c62c9706 100644
--- a/include/hyperv/hvhdk.h
+++ b/include/hyperv/hvhdk.h
@@ -79,6 +79,7 @@ struct hv_vp_register_page {
 
 		u64 registers[18];
 	};
+	u8 reserved[8];
 	/* Volatile XMM registers (HV_X64_REGISTER_CLASS_XMM) */
 	union {
 		struct {
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index 964f1be8150c..734b7ef98f4d 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -1304,7 +1304,11 @@ static inline void *hv_get_drvdata(struct hv_device *dev)
 
 struct device *hv_get_vmbus_root_device(void);
 
+#if IS_ENABLED(CONFIG_HYPERV_VMBUS)
 bool hv_vmbus_exists(void);
+#else
+static inline bool hv_vmbus_exists(void) { return false; }
+#endif
 
 struct hv_ring_buffer_debug_info {
 	u32 current_interrupt_mask;
@@ -1336,6 +1340,9 @@ int vmbus_allocate_mmio(struct resource **new, struct hv_device *device_obj,
 			bool fb_overlap_ok);
 void vmbus_free_mmio(resource_size_t start, resource_size_t size);
 
+void vmbus_initiate_unload(bool crash);
+void vmbus_set_skip_unload(bool skip);
+
 /*
  * GUID definitions of various offer types - services offered to the guest.
  */