Pull powerpc fixes from Michael Ellerman:
 "Three commits fixing some issues introduced with the recent IOMMU
  changes we merged.

  Thanks to Alexey Kardashevskiy"

* tag 'powerpc-5.15-6' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux:
  powerpc/pseries/iommu: Create huge DMA window if no MMIO32 is present
  powerpc/pseries/iommu: Check if the default window in use before removing it
  powerpc/pseries/iommu: Use correct vfree for it_map

The iommu_init_table() helper takes an address range to reserve in
the IOMMU table being initialized to exclude MMIO addresses, this is
useful if the window stretches far beyond 4GB (although wastes some TCEs).
At the moment the code searches for such MMIO32 range and fails if none
found which is considered a problem while it really is not: it is actually
better as this says there is no MMIO32 to reserve and we can use
usually wasted TCEs. Furthermore PHYP never actually allows creating
windows starting at busaddress=0 so this MMIO32 range is never useful.

This removes error exit and initializes the table with zero range if
no MMIO32 is detected.

Fixes: 381ceda88c4c ("powerpc/pseries/iommu: Make use of DDW for indirect mapping")
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211020132315.2287178-5-aik@ozlabs.ru

At the moment this check is performed after we remove the default window
which is late and disallows to revert whatever changes enable_ddw()
has made to DMA windows.

This moves the check and error exit before removing the window.

This raised the message severity from "debug" to "warning" as this
should not happen in practice and cannot be triggered by the userspace.

Fixes: 381ceda88c4c ("powerpc/pseries/iommu: Make use of DDW for indirect mapping")
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211020132315.2287178-4-aik@ozlabs.ru

The it_map array is vzalloc'ed so use vfree() for it when creating
a huge DMA window failed for whatever reason.

While at this, write zero to it_map.

Fixes: 381ceda88c4c ("powerpc/pseries/iommu: Make use of DDW for indirect mapping")
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211020132315.2287178-3-aik@ozlabs.ru

Pull powerpc fixes from Michael Ellerman:

 - Fix a bug exposed by a previous fix, where running guests with
   certain SMT topologies could crash the host on Power8.

 - Fix atomic sleep warnings when re-onlining CPUs, when PREEMPT is
   enabled.

Thanks to Nathan Lynch, Srikar Dronamraju, and Valentin Schneider.

* tag 'powerpc-5.15-5' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux:
  powerpc/smp: do not decrement idle task preempt count in CPU offline
  powerpc/idle: Don't corrupt back chain when going idle

With PREEMPT_COUNT=y, when a CPU is offlined and then onlined again, we
get:

BUG: scheduling while atomic: swapper/1/0/0x00000000
no locks held by swapper/1/0.
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.15.0-rc2+ #100
Call Trace:
 dump_stack_lvl+0xac/0x108
 __schedule_bug+0xac/0xe0
 __schedule+0xcf8/0x10d0
 schedule_idle+0x3c/0x70
 do_idle+0x2d8/0x4a0
 cpu_startup_entry+0x38/0x40
 start_secondary+0x2ec/0x3a0
 start_secondary_prolog+0x10/0x14

This is because powerpc's arch_cpu_idle_dead() decrements the idle task's
preempt count, for reasons explained in commit a7c2bb8279d2 ("powerpc:
Re-enable preemption before cpu_die()"), specifically "start_secondary()
expects a preempt_count() of 0."

However, since commit 2c669ef6979c ("powerpc/preempt: Don't touch the idle
task's preempt_count during hotplug") and commit f1a0a376ca0c ("sched/core:
Initialize the idle task with preemption disabled"), that justification no
longer holds.

The idle task isn't supposed to re-enable preemption, so remove the
vestigial preempt_enable() from the CPU offline path.

Tested with pseries and powernv in qemu, and pseries on PowerVM.

Fixes: 2c669ef6979c ("powerpc/preempt: Don't touch the idle task's preempt_count during hotplug")
Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211015173902.2278118-1-nathanl@linux.ibm.com

In isa206_idle_insn_mayloss() we store various registers into the stack
red zone, which is allowed.

However inside the IDLE_STATE_ENTER_SEQ_NORET macro we save r2 again,
to 0(r1), which corrupts the stack back chain.

We used to do the same in isa206_idle_insn_mayloss() itself, but we
fixed that in 73287caa9210 ("powerpc64/idle: Fix SP offsets when saving
GPRs"), however we missed that the macro also corrupts the back chain.

Corrupting the back chain is bad for debuggability but doesn't
necessarily cause a bug.

However we recently changed the stack handling in some KVM code, and it
now relies on the stack back chain being valid when it returns. The
corruption causes that code to return with r1 pointing somewhere in
kernel data, at some point LR is restored from the stack and we branch
to NULL or somewhere else invalid.

Only affects Power8 hosts running KVM guests, with dynamic_mt_modes
enabled (which it is by default).

The fixes tag below points to the commit that changed the KVM stack
handling, exposing this bug. The actual corruption of the back chain has
always existed since 948cf67c4726 ("powerpc: Add NAP mode support on
Power7 in HV mode").

Fixes: 9b4416c5095c ("KVM: PPC: Book3S HV: Fix stack handling in idle_kvm_start_guest()")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211020094826.3222052-1-mpe@ellerman.id.au

Pull powerpc fixes from Michael Ellerman:

 - Fix a bug where guests on P9 with interrupts passed through could get
   stuck in synchronize_irq().

 - Fix a bug in KVM on P8 where secondary threads entering a guest would
   write outside their allocated stack.

 - Fix a bug in KVM on P8 where secondary threads could confuse the host
   offline code and cause the guest or host to crash.

Thanks to Cédric Le Goater.

* tag 'powerpc-5.15-4' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux:
  KVM: PPC: Book3S HV: Make idle_kvm_start_guest() return 0 if it went to guest
  KVM: PPC: Book3S HV: Fix stack handling in idle_kvm_start_guest()
  powerpc/xive: Discard disabled interrupts in get_irqchip_state()

We call idle_kvm_start_guest() from power7_offline() if the thread has
been requested to enter KVM. We pass it the SRR1 value that was returned
from power7_idle_insn() which tells us what sort of wakeup we're
processing.

Depending on the SRR1 value we pass in, the KVM code might enter the
guest, or it might return to us to do some host action if the wakeup
requires it.

If idle_kvm_start_guest() is able to handle the wakeup, and enter the
guest it is supposed to indicate that by returning a zero SRR1 value to
us.

That was the behaviour prior to commit 10d91611f426 ("powerpc/64s:
Reimplement book3s idle code in C"), however in that commit the
handling of SRR1 was reworked, and the zeroing behaviour was lost.

Returning from idle_kvm_start_guest() without zeroing the SRR1 value can
confuse the host offline code, causing the guest to crash and other
weirdness.

Fixes: 10d91611f426 ("powerpc/64s: Reimplement book3s idle code in C")
Cc: stable@vger.kernel.org # v5.2+
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211015133929.832061-2-mpe@ellerman.id.au

In commit 10d91611f426 ("powerpc/64s: Reimplement book3s idle code in
C") kvm_start_guest() became idle_kvm_start_guest(). The old code
allocated a stack frame on the emergency stack, but didn't use the
frame to store anything, and also didn't store anything in its caller's
frame.

idle_kvm_start_guest() on the other hand is written more like a normal C
function, it creates a frame on entry, and also stores CR/LR into its
callers frame (per the ABI). The problem is that there is no caller
frame on the emergency stack.

The emergency stack for a given CPU is allocated with:

  paca_ptrs[i]->emergency_sp = alloc_stack(limit, i) + THREAD_SIZE;

So emergency_sp actually points to the first address above the emergency
stack allocation for a given CPU, we must not store above it without
first decrementing it to create a frame. This is different to the
regular kernel stack, paca->kstack, which is initialised to point at an
initial frame that is ready to use.

idle_kvm_start_guest() stores the backchain, CR and LR all of which
write outside the allocation for the emergency stack. It then creates a
stack frame and saves the non-volatile registers. Unfortunately the
frame it creates is not large enough to fit the non-volatiles, and so
the saving of the non-volatile registers also writes outside the
emergency stack allocation.

The end result is that we corrupt whatever is at 0-24 bytes, and 112-248
bytes above the emergency stack allocation.

In practice this has gone unnoticed because the memory immediately above
the emergency stack happens to be used for other stack allocations,
either another CPUs mc_emergency_sp or an IRQ stack. See the order of
calls to irqstack_early_init() and emergency_stack_init().

The low addresses of another stack are the top of that stack, and so are
only used if that stack is under extreme pressue, which essentially
never happens in practice - and if it did there's a high likelyhood we'd
crash due to that stack overflowing.

Still, we shouldn't be corrupting someone else's stack, and it is purely
luck that we aren't corrupting something else.

To fix it we save CR/LR into the caller's frame using the existing r1 on
entry, we then create a SWITCH_FRAME_SIZE frame (which has space for
pt_regs) on the emergency stack with the backchain pointing to the
existing stack, and then finally we switch to the new frame on the
emergency stack.

Fixes: 10d91611f426 ("powerpc/64s: Reimplement book3s idle code in C")
Cc: stable@vger.kernel.org # v5.2+
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211015133929.832061-1-mpe@ellerman.id.au