KVM: x86/pmu: Snapshot and clear reprogramming bitmap before reprogramming

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Refactor the handling of the reprogramming bitmap to snapshot and clear
to-be-processed bits before doing the reprogramming, and then explicitly
set bits for PMCs that need to be reprogrammed (again).  This will allow
adding a macro to iterate over all valid PMCs without having to add
special handling for the reprogramming bit, which (a) can have bits set
for non-existent PMCs and (b) needs to clear such bits to avoid wasting
cycles in perpetuity.

Note, the existing behavior of clearing bits after reprogramming does NOT
have a race with kvm_vm_ioctl_set_pmu_event_filter().  Setting a new PMU
filter synchronizes SRCU _before_ setting the bitmap, i.e. guarantees that
the vCPU isn't in the middle of reprogramming with a stale filter prior to
setting the bitmap.

Link: https://lore.kernel.org/r/20231110022857.1273836-5-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

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This commit is contained in:

Sean Christopherson 2023-11-09 18:28:51 -08:00

parent b31880ca2f

commit 004a0aa56e

2 changed files with 30 additions and 23 deletions

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arch/x86/include/asm/kvm_host.h

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52

arch/x86/kvm/pmu.c

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