On Tue, Jul 09, 2024, Manali Shukla wrote: > Malicious guests can cause bus locks to degrade the performance of I would say "misbehaving", I bet the overwhelming majority of bus locks in practice are due to legacy/crusty software, not malicious software. > a system. Non-WB(write-back) and misaligned locked > RMW(read-modify-write) instructions are referred to as "bus locks" and > require system wide synchronization among all processors to guarantee > atomicity. The bus locks may incur significant performance penalties > for all processors in the system. > > The Bus Lock Threshold feature proves beneficial for hypervisors > seeking to restrict guests' ability to initiate numerous bus locks, > thereby preventing system slowdowns that affect all tenants. None of this actually says what the feature does. > Presence of the Bus Lock threshold feature is indicated via CPUID > function 0x8000000A_EDX[29] > > Signed-off-by: Manali Shukla <manali.shukla@xxxxxxx> > --- > arch/x86/include/asm/cpufeatures.h | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h > index 3c7434329661..10f397873790 100644 > --- a/arch/x86/include/asm/cpufeatures.h > +++ b/arch/x86/include/asm/cpufeatures.h > @@ -381,6 +381,7 @@ > #define X86_FEATURE_V_SPEC_CTRL (15*32+20) /* Virtual SPEC_CTRL */ > #define X86_FEATURE_VNMI (15*32+25) /* Virtual NMI */ > #define X86_FEATURE_SVME_ADDR_CHK (15*32+28) /* "" SVME addr check */ > +#define X86_FEATURE_BUS_LOCK_THRESHOLD (15*32+29) /* "" Bus lock threshold */ I would strongly prefer to enumerate this in /proc/cpuinfo, having to manually query CPUID to see if a CPU supports a feature I want to test is beyond annoying. > /* Intel-defined CPU features, CPUID level 0x00000007:0 (ECX), word 16 */ > #define X86_FEATURE_AVX512VBMI (16*32+ 1) /* AVX512 Vector Bit Manipulation instructions*/ > > base-commit: 704ec48fc2fbd4e41ec982662ad5bf1eee33eeb2 > -- > 2.34.1 >
