linux.git/arch/x86/kernel/kvmclock.c, branch v6.6

x86/tsc: Provide sched_clock_noinstr()

2023-06-05T19:11:08+00:00

With the intent to provide local_clock_noinstr(), a variant of
local_clock() that's safe to be called from noinstr code (with the
assumption that any such code will already be non-preemptible),
prepare for things by providing a noinstr sched_clock_noinstr()
function.

Specifically, preempt_enable_*() calls out to schedule(), which upsets
noinstr validation efforts.

  vmlinux.o: warning: objtool: native_sched_clock+0x96: call to preempt_schedule_notrace_thunk() leaves .noinstr.text section
  vmlinux.o: warning: objtool: kvm_clock_read+0x22: call to preempt_schedule_notrace_thunk() leaves .noinstr.text section

Signed-off-by: Peter Zijlstra (Intel) 
Tested-by: Michael Kelley   # Hyper-V
Link: https://lore.kernel.org/r/20230519102715.910937674@infradead.org

sched/clock/x86: Mark sched_clock() noinstr

2023-01-31T14:01:47+00:00

In order to use sched_clock() from noinstr code, mark it and all it's
implenentations noinstr.

The whole pvclock thing (used by KVM/Xen) is a bit of a pain,
since it calls out to watchdogs, create a
pvclock_clocksource_read_nowd() variant doesn't do that and can be
noinstr.

Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Ingo Molnar 
Link: https://lore.kernel.org/r/20230126151323.702003578@infradead.org

x86/kvm: Don't waste kvmclock memory if there is nopv parameter

2022-04-13T17:37:19+00:00

When the "nopv" command line parameter is used, it should not waste
memory for kvmclock.

Signed-off-by: Wanpeng Li 
Message-Id: <1646727529-11774-1-git-send-email-wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini

x86/kvmclock: Fix Hyper-V Isolated VM's boot issue when vCPUs > 64

2022-02-25T15:09:34+00:00

When Linux runs as an Isolated VM on Hyper-V, it supports AMD SEV-SNP
but it's partially enlightened, i.e. cc_platform_has(
CC_ATTR_GUEST_MEM_ENCRYPT) is true but sev_active() is false.

Commit 4d96f9109109 per se is good, but with it now
kvm_setup_vsyscall_timeinfo() -> kvmclock_init_mem() calls
set_memory_decrypted(), and later gets stuck when trying to zere out
the pages pointed by 'hvclock_mem', if Linux runs as an Isolated VM on
Hyper-V. The cause is that here now the Linux VM should no longer access
the original guest physical addrss (GPA); instead the VM should do
memremap() and access the original GPA + ms_hyperv.shared_gpa_boundary:
see the example code in drivers/hv/connection.c: vmbus_connect() or
drivers/hv/ring_buffer.c: hv_ringbuffer_init(). If the VM tries to
access the original GPA, it keepts getting injected a fault by Hyper-V
and gets stuck there.

Here the issue happens only when the VM has >=65 vCPUs, because the
global static array hv_clock_boot[] can hold 64 "struct
pvclock_vsyscall_time_info" (the sizeof of the struct is 64 bytes), so
kvmclock_init_mem() only allocates memory in the case of vCPUs > 64.

Since the 'hvclock_mem' pages are only useful when the kvm clock is
supported by the underlying hypervisor, fix the issue by returning
early when Linux VM runs on Hyper-V, which doesn't support kvm clock.

Fixes: 4d96f9109109 ("x86/sev: Replace occurrences of sev_active() with cc_platform_has()")
Tested-by: Andrea Parri (Microsoft) 
Signed-off-by: Andrea Parri (Microsoft) 
Signed-off-by: Dexuan Cui 
Message-Id: <20220225084600.17817-1-decui@microsoft.com>
Signed-off-by: Paolo Bonzini

x86/kvm: Don't waste memory if kvmclock is disabled

2022-02-25T15:09:34+00:00

Even if "no-kvmclock" is passed in cmdline parameter, the guest kernel
still allocates hvclock_mem which is scaled by the number of vCPUs,
let's check kvmclock enable in advance to avoid this memory waste.

Signed-off-by: Wanpeng Li 
Message-Id: <1645520523-30814-1-git-send-email-wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini

x86/kvm: Silence per-cpu pr_info noise about KVM clocks and steal time

2022-01-07T15:44:43+00:00

I made the actual CPU bringup go nice and fast... and then Linux spends
half a minute printing stupid nonsense about clocks and steal time for
each of 256 vCPUs. Don't do that. Nobody cares.

Signed-off-by: David Woodhouse 
Message-Id: <20211209150938.3518-12-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini

x86/sev: Replace occurrences of sev_active() with cc_platform_has()

2021-10-04T09:46:58+00:00

Replace uses of sev_active() with the more generic cc_platform_has()
using CC_ATTR_GUEST_MEM_ENCRYPT. If future support is added for other
memory encryption technologies, the use of CC_ATTR_GUEST_MEM_ENCRYPT
can be updated, as required.

Signed-off-by: Tom Lendacky 
Signed-off-by: Borislav Petkov 
Link: https://lkml.kernel.org/r/20210928191009.32551-7-bp@alien8.de

x86/kvmclock: Move this_cpu_pvti into kvmclock.h

2021-09-30T08:08:01+00:00

There're other modules might use hv_clock_per_cpu variable like ptp_kvm,
so move it into kvmclock.h and export the symbol to make it visiable to
other modules.

Signed-off-by: Zelin Deng 
Cc: 
Message-Id: <1632892429-101194-2-git-send-email-zelin.deng@linux.alibaba.com>
Signed-off-by: Paolo Bonzini

x86/kvm: Disable all PV features on crash

2021-05-07T10:06:10+00:00

Crash shutdown handler only disables kvmclock and steal time, other PV
features remain active so we risk corrupting memory or getting some
side-effects in kdump kernel. Move crash handler to kvm.c and unify
with CPU offline.

Signed-off-by: Vitaly Kuznetsov 
Message-Id: <20210414123544.1060604-5-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini

x86/kvm: Disable kvmclock on all CPUs on shutdown

2021-05-07T10:06:10+00:00

Currenly, we disable kvmclock from machine_shutdown() hook and this
only happens for boot CPU. We need to disable it for all CPUs to
guard against memory corruption e.g. on restore from hibernate.

Note, writing '0' to kvmclock MSR doesn't clear memory location, it
just prevents hypervisor from updating the location so for the short
while after write and while CPU is still alive, the clock remains usable
and correct so we don't need to switch to some other clocksource.

Signed-off-by: Vitaly Kuznetsov 
Message-Id: <20210414123544.1060604-4-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini