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perf/x86/core: Zero @lbr instead of returning -1 in x86_perf_get_lbr() stub

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Drop the return value from x86_perf_get_lbr() and have the stub zero out
the @lbr structure instead of returning -1 to indicate "no LBR support".
KVM doesn't actually check the return value, and instead subtly relies on
zeroing the number of LBRs in intel_pmu_init().

Formalize "nr=0 means unsupported" so that KVM doesn't need to add a
pointless check on the return value to fix KVM's benign bug.

Note, the stub is necessary even though KVM x86 selects PERF_EVENTS and
the caller exists only when CONFIG_KVM_INTEL=y.  Despite the name,
KVM_INTEL doesn't strictly require CPU_SUP_INTEL, it can be built with
any of INTEL || CENTAUR || ZHAOXIN CPUs.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20221006000314.73240-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson
2022-10-06 00:03:07 +00:00
committed by Paolo Bonzini
parent d72cf8ffe4
commit 0b9ca98b72
3 changed files with 6 additions and 9 deletions
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6
arch/x86/include/asm/perf_event.h
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@@ -543,12 +543,12 @@ static inline void perf_check_microcode(void) { }
#if defined(CONFIG_PERF_EVENTS) && defined(CONFIG_CPU_SUP_INTEL)
extern struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr, void *data);
extern int x86_perf_get_lbr(struct x86_pmu_lbr *lbr);
extern void x86_perf_get_lbr(struct x86_pmu_lbr *lbr);
#else
struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr, void *data);
static inline int x86_perf_get_lbr(struct x86_pmu_lbr *lbr)
static inline void x86_perf_get_lbr(struct x86_pmu_lbr *lbr)
{
return -1;
memset(lbr, 0, sizeof(*lbr));
}
#endif