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KVM: x86/pmu: Avoid CPL lookup if PMC enabline for USER and KERNEL is the same

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Don't bother querying the CPL if a PMC is (not) counting for both USER and
KERNEL, i.e. if the end result is guaranteed to be the same regardless of
the CPL.  Querying the CPL on Intel requires a VMREAD, i.e. isn't free,
and a single CMP+Jcc is cheap.

Link: https://lore.kernel.org/r/20231110022857.1273836-11-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2023-11-09 18:28:57 -08:00
parent e35529fb4a
commit 83bdfe04c9
1 changed files with 7 additions and 0 deletions
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7
arch/x86/kvm/pmu.c
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@ -838,6 +838,13 @@ static inline bool cpl_is_matched(struct kvm_pmc *pmc)
select_user = config & 0x2;
}
/*
* Skip the CPL lookup, which isn't free on Intel, if the result will
* be the same regardless of the CPL.
*/
if (select_os == select_user)
return select_os;
return (static_call(kvm_x86_get_cpl)(pmc->vcpu) == 0) ? select_os : select_user;
}