Hi Boris, On 3/25/2025 3:26 AM, Borislav Petkov wrote: > On Mon, Mar 24, 2025 at 01:02:45PM +0000, Manali Shukla wrote: >> Misbehaving guests can cause bus locks to degrade the performance of >> the system. The Bus Lock Threshold feature can be used to address this >> issue by providing capability to the hypervisor to limit guest's >> ability to generate bus lock, thereby preventing system slowdown due >> to performance penalities. >> >> When the Bus Lock Threshold feature is enabled, the processor checks >> the bus lock threshold count before executing the buslock and decides >> whether to trigger bus lock exit or not. >> >> The value of the bus lock threshold count '0' generates bus lock >> exits, and if the value is greater than '0', the bus lock is executed >> successfully and the bus lock threshold count is decremented. >> >> 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 8f8aaf94dc00..a3ab8d1f5c17 100644 >> --- a/arch/x86/include/asm/cpufeatures.h >> +++ b/arch/x86/include/asm/cpufeatures.h >> @@ -386,6 +386,7 @@ >> #define X86_FEATURE_V_SPEC_CTRL (15*32+20) /* "v_spec_ctrl" Virtual SPEC_CTRL */ >> #define X86_FEATURE_VNMI (15*32+25) /* "vnmi" Virtual NMI */ >> #define X86_FEATURE_SVME_ADDR_CHK (15*32+28) /* SVME addr check */ >> +#define X86_FEATURE_BUS_LOCK_THRESHOLD (15*32+29) /* "buslock" Bus lock threshold */ > ^^^^^^^^^ > > Please read this before you do stuff like that: > > Documentation/arch/x86/cpuinfo.rst > > Thx. > Do you have concern with the decision to expose the flag to /proc/cpuinfo? The decision to expose the flag to /proc/cpuinfo was already discussed in [v1]. As suggested in the discussion [v1], I have added "buslock" to be enumerated in /proc/cpuinfo. However, if your concern is with the name, I can change the exposed name from "buslock" to "bus_lock_threshold". - Manali
