Messages in this thread | | | Date | Tue, 27 Jun 2023 18:57:28 +0800 | Subject | Re: [EXTERNAL] Re: [PATCH 5/9] x86/hyperv: Use vmmcall to implement Hyper-V hypercall in sev-snp enlightened guest | From | Tianyu Lan <> |
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On 6/8/2023 11:15 PM, Tianyu Lan wrote: > On 6/8/2023 9:21 PM, Peter Zijlstra wrote: >> On Thu, Jun 01, 2023 at 11:16:18AM -0400, Tianyu Lan wrote: >>> From: Tianyu Lan <tiala@microsoft.com> >>> >>> In sev-snp enlightened guest, Hyper-V hypercall needs >>> to use vmmcall to trigger vmexit and notify hypervisor >>> to handle hypercall request. >>> >>> There is no x86 SEV SNP feature flag support so far and >>> hardware provides MSR_AMD64_SEV register to check SEV-SNP >>> capability with MSR_AMD64_SEV_ENABLED bit. ALTERNATIVE can't >>> work without SEV-SNP x86 feature flag. May add later when >>> the associated flag is introduced. >>> >>> Signed-off-by: Tianyu Lan <tiala@microsoft.com> >>> --- >>> arch/x86/include/asm/mshyperv.h | 44 ++++++++++++++++++++++++--------- >>> 1 file changed, 33 insertions(+), 11 deletions(-) >>> >>> diff --git a/arch/x86/include/asm/mshyperv.h >>> b/arch/x86/include/asm/mshyperv.h >>> index 31c476f4e656..d859d7c5f5e8 100644 >>> --- a/arch/x86/include/asm/mshyperv.h >>> +++ b/arch/x86/include/asm/mshyperv.h >>> @@ -61,16 +61,25 @@ static inline u64 hv_do_hypercall(u64 control, >>> void *input, void *output) >>> u64 hv_status; >>> #ifdef CONFIG_X86_64 >>> - if (!hv_hypercall_pg) >>> - return U64_MAX; >>> + if (hv_isolation_type_en_snp()) { >>> + __asm__ __volatile__("mov %4, %%r8\n" >>> + "vmmcall" >>> + : "=a" (hv_status), ASM_CALL_CONSTRAINT, >>> + "+c" (control), "+d" (input_address) >>> + : "r" (output_address) >>> + : "cc", "memory", "r8", "r9", "r10", "r11"); >>> + } else { >>> + if (!hv_hypercall_pg) >>> + return U64_MAX; >>> - __asm__ __volatile__("mov %4, %%r8\n" >>> - CALL_NOSPEC >>> - : "=a" (hv_status), ASM_CALL_CONSTRAINT, >>> - "+c" (control), "+d" (input_address) >>> - : "r" (output_address), >>> - THUNK_TARGET(hv_hypercall_pg) >>> - : "cc", "memory", "r8", "r9", "r10", "r11"); >>> + __asm__ __volatile__("mov %4, %%r8\n" >>> + CALL_NOSPEC >>> + : "=a" (hv_status), ASM_CALL_CONSTRAINT, >>> + "+c" (control), "+d" (input_address) >>> + : "r" (output_address), >>> + THUNK_TARGET(hv_hypercall_pg) >>> + : "cc", "memory", "r8", "r9", "r10", "r11"); >>> + } >>> #else >> >> Remains unanswered: >> >> https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Flkml.kernel.org%2Fr%2F20230516102912.GG2587705%2540hirez.programming.kicks-ass.net&data=05%7C01%7CTianyu.Lan%40microsoft.com%7C60a576eb67634ffa27b108db68234d5a%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C638218273105649705%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=MFj67DON0K%2BUoUJbeaIA5oVTxyrzO3fb5DbxYgDWwX0%3D&reserved=0 >> >> Would this not generate better code with an alternative? > > > Hi Peter: > Thanks to review. I put the explaination in the change log. > > "There is no x86 SEV SNP feature(X86_FEATURE_SEV_SNP) flag > support so far and hardware provides MSR_AMD64_SEV register > to check SEV-SNP capability with MSR_AMD64_SEV_ENABLED bit > ALTERNATIVE can't work without SEV-SNP x86 feature flag." > There is no cpuid leaf bit to check AMD SEV-SNP feature. > > After some Hyper-V doesn't provides SEV and SEV-ES guest before and so > may reuse X86_FEATURE_SEV and X86_FEATURE_SEV_ES flag as alternative > feature check for Hyper-V SEV-SNP guest. Will refresh patch. >
Hi Peter: I tried using alternative for "vmmcall" and CALL_NOSPEC in a single Inline assembly. The output is different in the SEV-SNP mode. When SEV- SNP is enabled, thunk_target is not required. While it's necessary in the non SEV-SNP mode. Do you have any idea how to differentiate outputs in the single Inline assembly which just like alternative works for assembler template.
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