[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 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. Jan
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