[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v2 4/4] x86/spec-ctrl: Fix NMI race condition with VT-x MSR_SPEC_CTRL handling
On 20/01/2022 08:14, Jan Beulich wrote: > On 19.01.2022 18:00, Andrew Cooper wrote: >> On 19/01/2022 13:42, Jan Beulich wrote: >>> On 17.01.2022 19:34, Andrew Cooper wrote: >>>> --- a/xen/arch/x86/hvm/vmx/entry.S >>>> +++ b/xen/arch/x86/hvm/vmx/entry.S >>>> @@ -35,7 +35,14 @@ ENTRY(vmx_asm_vmexit_handler) >>>> >>>> /* SPEC_CTRL_ENTRY_FROM_VMX Req: b=curr %rsp=regs/cpuinfo, >>>> Clob: acd */ >>>> ALTERNATIVE "", DO_OVERWRITE_RSB, X86_FEATURE_SC_RSB_HVM >>>> - ALTERNATIVE "", DO_SPEC_CTRL_ENTRY_FROM_HVM, >>>> X86_FEATURE_SC_MSR_HVM >>>> + >>>> + .macro restore_spec_ctrl >>>> + mov $MSR_SPEC_CTRL, %ecx >>>> + movzbl CPUINFO_xen_spec_ctrl(%rsp), %eax >>>> + xor %edx, %edx >>>> + wrmsr >>>> + .endm >>>> + ALTERNATIVE "", restore_spec_ctrl, X86_FEATURE_SC_MSR_HVM >>>> /* WARNING! `ret`, `call *`, `jmp *` not safe before this point. >>>> */ >>>> >>>> /* Hardware clears MSR_DEBUGCTL on VMExit. Reinstate it if >>>> debugging Xen. */ >>>> @@ -82,8 +89,7 @@ UNLIKELY_END(realmode) >>>> mov VCPUMSR_spec_ctrl_raw(%rax), %eax >>>> >>>> /* WARNING! `ret`, `call *`, `jmp *` not safe beyond this point. >>>> */ >>>> - /* SPEC_CTRL_EXIT_TO_VMX Req: a=spec_ctrl %rsp=regs/cpuinfo, >>>> Clob: cd */ >>>> - ALTERNATIVE "", DO_SPEC_CTRL_EXIT_TO_GUEST, X86_FEATURE_SC_MSR_HVM >>>> + /* SPEC_CTRL_EXIT_TO_VMX Req: %rsp=regs/cpuinfo >>>> Clob: */ >>>> ALTERNATIVE "", __stringify(verw CPUINFO_verw_sel(%rsp)), >>>> X86_FEATURE_SC_VERW_HVM >>> I notice you did update this clobber remark, but what about the one further >>> up in context? >> What about it? It still clobbers %eax, %ecx and %edx. > Oh, sorry - I did look at DO_OVERWRITE_RSB only, not paying attention > to the now open-coded 2nd part, which - due to the blank line - doesn't > appear connected to the comment anymore. Yeah - it's a little harder now that it isn't a single line. The req/clob information really is most useful at the start of the block, because that's where it is important to get the context correct. Can I take this as an R-by then? ~Andrew
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