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[PATCH v6 5/8] x86/hyperv: Use vmmcall to implement Hyper-V hypercall in sev-snp enlightened guest

Tianyu Lan posted 8 patches 2 years, 4 months ago
There is a newer version of this series
[PATCH v6 5/8] x86/hyperv: Use vmmcall to implement Hyper-V hypercall in sev-snp enlightened guest
Posted by Tianyu Lan 2 years, 4 months ago 
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.

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 9f11f0495950..8479626cd7cb 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -59,16 +59,25 @@ 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
 	u32 input_address_hi = upper_32_bits(input_address);
 	u32 input_address_lo = lower_32_bits(input_address);
@@ -102,7 +111,13 @@ static inline u64 _hv_do_fast_hypercall8(u64 control, u64 input1)
 	u64 hv_status;
 
 #ifdef CONFIG_X86_64
-	{
+	if (hv_isolation_type_en_snp()) {
+		__asm__ __volatile__(
+				"vmmcall"
+				: "=a" (hv_status), ASM_CALL_CONSTRAINT,
+				"+c" (control), "+d" (input1)
+				:: "cc", "r8", "r9", "r10", "r11");
+	} else {
 		__asm__ __volatile__(CALL_NOSPEC
 				     : "=a" (hv_status), ASM_CALL_CONSTRAINT,
 				       "+c" (control), "+d" (input1)
@@ -147,7 +162,14 @@ static inline u64 _hv_do_fast_hypercall16(u64 control, u64 input1, u64 input2)
 	u64 hv_status;
 
 #ifdef CONFIG_X86_64
-	{
+	if (hv_isolation_type_en_snp()) {
+		__asm__ __volatile__("mov %4, %%r8\n"
+				     "vmmcall"
+				     : "=a" (hv_status), ASM_CALL_CONSTRAINT,
+				       "+c" (control), "+d" (input1)
+				     : "r" (input2)
+				     : "cc", "r8", "r9", "r10", "r11");
+	} else {
 		__asm__ __volatile__("mov %4, %%r8\n"
 				     CALL_NOSPEC
 				     : "=a" (hv_status), ASM_CALL_CONSTRAINT,
-- 
2.25.1
RE: [PATCH v6 5/8] x86/hyperv: Use vmmcall to implement Hyper-V hypercall in sev-snp enlightened guest
Posted by Dexuan Cui 2 years, 4 months ago 
> From: Tianyu Lan <ltykernel@gmail.com>
> Sent: Wednesday, August 16, 2023 8:59 AM
> [...]
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -59,16 +59,25 @@ 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()) {

I got a build failure:

In file included from arch/x86/hyperv/hv_spinlock.c:15:
./arch/x86/include/asm/mshyperv.h: In function 'hv_do_hypercall':
./arch/x86/include/asm/mshyperv.h:69:6: error: implicit declaration of function 'hv_isolation_type_en_snp' [-Werror=implicit-function-declaration]
   69 |  if (hv_isolation_type_en_snp()) {
      |      ^~~~~~~~~~~~~~~~~~~~~~~~

In arch/x86/include/asm/mshyperv.h, we do have 
	extern bool hv_isolation_type_en_snp(void);
but it's defined at a late place. I think we need to move it to before 
hv_do_hypercall().

We also have 
	extern bool hv_isolation_type_en_snp(void);
in include/asm-generic/mshyperv.h, but that header file
is included at the end of arch/x86/include/asm/mshyperv.h.


> +		__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");
RE: [PATCH v6 5/8] x86/hyperv: Use vmmcall to implement Hyper-V hypercall in sev-snp enlightened guest
Posted by Dexuan Cui 2 years, 4 months ago 
> From: Tianyu Lan <ltykernel@gmail.com>
> Sent: Wednesday, August 16, 2023 8:59 AM
> To: KY Srinivasan <kys@microsoft.com>; Haiyang Zhang
> <haiyangz@microsoft.com>; wei.liu@kernel.org; Dexuan Cui
>  [...]
> In sev-snp enlightened guest, Hyper-V hypercall needs
> to use vmmcall to trigger vmexit and notify hypervisor
> to handle hypercall request.
> 
> Signed-off-by: Tianyu Lan <tiala@microsoft.com>
> ---
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -59,16 +59,25 @@ 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");
> +	}

IMO it's better if we add a "return hv_status;" for the SNP case, and don't move
the assembly code for the regular VM. I made a patch:
https://github.com/dcui/tdx/commit/f81013578605aa02939a3186afa9fc76791b3acd

You may want to explain briefly why the earlier approach 
	ALTERNATIVE(CALL_NOSPEC, "vmmcall", X86_FEATURE_SEV_ES)
doesn't work:

start_kernel() calls hyperv_init() before alternative_instructions(), and hyperv_init() 
already uses hypercalls, e.g. the newly-added get_vtl() in your patch 2.

start_kernel:
  late_time_init
    x86_late_time_init
      x86_init.irqs.intr_mode_init
        apic_intr_mode_init
          x86_platform.apic_post_init
            hyperv_init ==> it already uses hypercalls, e.g. the newly-added get_vtl() in your patch 2.

  arch_cpu_finalize_init()
    alternative_instructions()

We can move the get_vtl hypercall to a later place, but there are also
other hypercalls before alternative_instructions(). IMO it may be unsafe
to run ALTERNATIVE code before  alternative_instructions() is called.

Patchew 2.1-devel-b67e4c2

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