On Thu, Aug 29, 2024 at 03:28:13PM -0700, Dave Hansen wrote: > On 7/11/24 15:03, Pawan Gupta wrote: > > +/* > > + * Safer version of CLEAR_CPU_BUFFERS that uses %ss to reference VERW operand > > + * mds_verw_sel. This ensures VERW will not #GP for an arbitrary user %ds. > > + */ > > +.macro CLEAR_CPU_BUFFERS_SAFE > > + ALTERNATIVE "", __stringify(verw %ss:_ASM_RIP(mds_verw_sel)), X86_FEATURE_CLEAR_CPU_BUF > > +.endm > > One other thing... > > Instead of making a "_SAFE" variant, let's just make the 32-bit version > always safe. That sounds good to me. > Also, is there any downside to using %ss: on 64-bit? If not, let's just > update the one and only CLEAR_CPU_BUFFERS use %ss:. A quick test after adding %ss: on 64-bit doesn't show any significant latency difference. I will revise the patch.
