From: Tianyu Lan <Tianyu.Lan@microsoft.com>

Hyper-V Isolation VM code uses sev_es_ghcb_hv_call() to read/write MSR
via ghcb page. The SEV-ES guest should call the sev_es_negotiate_protocol()
to negotiate the GHCB protocol version before establishing the GHCB. Call
sev_es_negotiate_protocol() in the hyperv_init_ghcb().

Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
---
This patch based on the "Add AMD Secure Nested Paging (SEV-SNP) Guest Support"
patchset. https://lore.kernel.org/lkml/20220128171804.569796-1-brijesh.singh@amd.com/

 arch/x86/hyperv/hv_init.c    | 6 ++++++
 arch/x86/include/asm/sev.h   | 2 ++
 arch/x86/kernel/sev-shared.c | 2 +-
 arch/x86/kernel/sev.c        | 4 ++--
 4 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 24f4a06ac46a..a22303fccf02 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -28,6 +28,7 @@
 #include <linux/syscore_ops.h>
 #include <clocksource/hyperv_timer.h>
 #include <linux/highmem.h>
+#include <asm/sev.h>
 
 int hyperv_init_cpuhp;
 u64 hv_current_partition_id = ~0ull;
@@ -69,6 +70,11 @@ static int hyperv_init_ghcb(void)
 	ghcb_base = (void **)this_cpu_ptr(hv_ghcb_pg);
 	*ghcb_base = ghcb_va;
 
+	sev_es_negotiate_protocol();
+
+	/* Write ghcb page back after negotiating protocol. */
+	wrmsrl(MSR_AMD64_SEV_ES_GHCB, ghcb_gpa);
+	VMGEXIT();
 	return 0;
 }
 
diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 7a5934af9d47..fc6b0c526492 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -120,6 +120,8 @@ extern enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb,
 					  struct es_em_ctxt *ctxt,
 					  u64 exit_code, u64 exit_info_1,
 					  u64 exit_info_2);
+extern bool sev_es_negotiate_protocol(void);
+
 static inline int rmpadjust(unsigned long vaddr, bool rmp_psize, unsigned long attrs)
 {
 	int rc;
diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index ce06cb7c8ed0..8b8af5a8d402 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -145,7 +145,7 @@ static void snp_register_ghcb_early(unsigned long paddr)
 		sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_REGISTER);
 }
 
-static bool sev_es_negotiate_protocol(void)
+bool sev_es_negotiate_protocol(void)
 {
 	u64 val;
 
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 3568b3303314..46c53c4885ee 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -167,12 +167,12 @@ void noinstr __sev_es_ist_exit(void)
 	this_cpu_write(cpu_tss_rw.x86_tss.ist[IST_INDEX_VC], *(unsigned long *)ist);
 }
 
-static inline u64 sev_es_rd_ghcb_msr(void)
+inline u64 sev_es_rd_ghcb_msr(void)
 {
 	return __rdmsr(MSR_AMD64_SEV_ES_GHCB);
 }
 
-static __always_inline void sev_es_wr_ghcb_msr(u64 val)
+__always_inline void sev_es_wr_ghcb_msr(u64 val)
 {
 	u32 low, high;
 
-- 
2.25.1

On Mon, Feb 07, 2022 at 11:09:28AM -0500, Tianyu Lan wrote:
> From: Tianyu Lan <Tianyu.Lan@microsoft.com>
> 
> Hyper-V Isolation VM code uses sev_es_ghcb_hv_call() to read/write MSR
> via ghcb page. The SEV-ES guest should call the sev_es_negotiate_protocol()
> to negotiate the GHCB protocol version before establishing the GHCB. Call
> sev_es_negotiate_protocol() in the hyperv_init_ghcb().
> 
> Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
> ---
> This patch based on the "Add AMD Secure Nested Paging (SEV-SNP) Guest Support"
> patchset. https://lore.kernel.org/lkml/20220128171804.569796-1-brijesh.singh@amd.com/
> 
>  arch/x86/hyperv/hv_init.c    | 6 ++++++
>  arch/x86/include/asm/sev.h   | 2 ++
>  arch/x86/kernel/sev-shared.c | 2 +-
>  arch/x86/kernel/sev.c        | 4 ++--
>  4 files changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> index 24f4a06ac46a..a22303fccf02 100644
> --- a/arch/x86/hyperv/hv_init.c
> +++ b/arch/x86/hyperv/hv_init.c
> @@ -28,6 +28,7 @@
>  #include <linux/syscore_ops.h>
>  #include <clocksource/hyperv_timer.h>
>  #include <linux/highmem.h>
> +#include <asm/sev.h>
>  
>  int hyperv_init_cpuhp;
>  u64 hv_current_partition_id = ~0ull;
> @@ -69,6 +70,11 @@ static int hyperv_init_ghcb(void)
>  	ghcb_base = (void **)this_cpu_ptr(hv_ghcb_pg);
>  	*ghcb_base = ghcb_va;
>  
> +	sev_es_negotiate_protocol();

The return value should be checked, right?

There is no logical connection between this function call and the wrmsrl
below. Is there new information available after calling
sev_es_negotiate_protocol?

> +
> +	/* Write ghcb page back after negotiating protocol. */
> +	wrmsrl(MSR_AMD64_SEV_ES_GHCB, ghcb_gpa);
> +	VMGEXIT();
>  	return 0;
>  }
>  
[...]
> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> index 3568b3303314..46c53c4885ee 100644
> --- a/arch/x86/kernel/sev.c
> +++ b/arch/x86/kernel/sev.c
> @@ -167,12 +167,12 @@ void noinstr __sev_es_ist_exit(void)
>  	this_cpu_write(cpu_tss_rw.x86_tss.ist[IST_INDEX_VC], *(unsigned long *)ist);
>  }
>  
> -static inline u64 sev_es_rd_ghcb_msr(void)
> +inline u64 sev_es_rd_ghcb_msr(void)
>  {
>  	return __rdmsr(MSR_AMD64_SEV_ES_GHCB);
>  }
>  
> -static __always_inline void sev_es_wr_ghcb_msr(u64 val)
> +__always_inline void sev_es_wr_ghcb_msr(u64 val)

Why are these needed? They are not used anywhere in this patch.

Thanks,
Wei.

>  {
>  	u32 low, high;
>  
> -- 
> 2.25.1
> 

Nits:

> Hyper-V Isolation VM code uses sev_es_ghcb_hv_call() to read/write MSR
> via ghcb page. The SEV-ES guest should call the sev_es_negotiate_protocol()

ghcb page -> GHCB page

call the sev_es_negotiate_protocol() -> call sev_es_negotiate_protocol()
	(or -- call the sev_es_negotiate_protocol() function)

> to negotiate the GHCB protocol version before establishing the GHCB. Call
> sev_es_negotiate_protocol() in the hyperv_init_ghcb().

in the hyperv_init_ghcb() -> in hyperv_init_ghcb()

(similarly elsewhere).

  Andrea