On 6/8/2023 11:15 PM, Tianyu Lan wrote:

On 6/8/2023 9:21 PM, Peter Zijlstra wrote:

quoted

On Thu, Jun 01, 2023 at 11:16:18AM -0400, Tianyu Lan wrote:

quoted

From: Tianyu Lan <redacted>

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 <redacted>
---
  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.