Re: [PATCH v7 09/45] x86/sev: Save the negotiated GHCB version

[Tianyu Lan <ltykernel@gmail.com>]

Hi Brijesh:
      We find this patch breaks AMD SEV support in the Hyper-V Isolation
VM. Hyper-V code also uses sev_es_ghcb_hv_call() to read or write msr
value. The sev_es_check_cpu_features() isn't called in the Hyper-V code
and so the ghcb_version is always 0. Could you add a new parameter 
ghcb_version for sev_es_ghcb_hv_call() and then caller may input 
ghcb_version?

Thanks.

On 11/11/2021 6:06 AM, Brijesh Singh wrote:
> The SEV-ES guest calls the sev_es_negotiate_protocol() to negotiate the
> GHCB protocol version before establishing the GHCB. Cache the negotiated
> GHCB version so that it can be used later.
> 
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> ---
>   arch/x86/include/asm/sev.h   |  2 +-
>   arch/x86/kernel/sev-shared.c | 17 ++++++++++++++---
>   2 files changed, 15 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> index ec060c433589..9b9c190e8c3b 100644
> --- a/arch/x86/include/asm/sev.h
> +++ b/arch/x86/include/asm/sev.h
> @@ -12,7 +12,7 @@
>   #include <asm/insn.h>
>   #include <asm/sev-common.h>
>   
> -#define GHCB_PROTO_OUR		0x0001UL
> +#define GHCB_PROTOCOL_MIN	1ULL
>   #define GHCB_PROTOCOL_MAX	1ULL
>   #define GHCB_DEFAULT_USAGE	0ULL
>   
> diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
> index 2abf8a7d75e5..91105f5a02a8 100644
> --- a/arch/x86/kernel/sev-shared.c
> +++ b/arch/x86/kernel/sev-shared.c
> @@ -14,6 +14,15 @@
>   #define has_cpuflag(f)	boot_cpu_has(f)
>   #endif
>   
> +/*
> + * Since feature negotiation related variables are set early in the boot
> + * process they must reside in the .data section so as not to be zeroed
> + * out when the .bss section is later cleared.
> + *
> + * GHCB protocol version negotiated with the hypervisor.
> + */
> +static u16 ghcb_version __ro_after_init;
> +
>   static bool __init sev_es_check_cpu_features(void)
>   {
>   	if (!has_cpuflag(X86_FEATURE_RDRAND)) {
> @@ -51,10 +60,12 @@ static bool sev_es_negotiate_protocol(void)
>   	if (GHCB_MSR_INFO(val) != GHCB_MSR_SEV_INFO_RESP)
>   		return false;
>   
> -	if (GHCB_MSR_PROTO_MAX(val) < GHCB_PROTO_OUR ||
> -	    GHCB_MSR_PROTO_MIN(val) > GHCB_PROTO_OUR)
> +	if (GHCB_MSR_PROTO_MAX(val) < GHCB_PROTOCOL_MIN ||
> +	    GHCB_MSR_PROTO_MIN(val) > GHCB_PROTOCOL_MAX)
>   		return false;
>   
> +	ghcb_version = min_t(size_t, GHCB_MSR_PROTO_MAX(val), GHCB_PROTOCOL_MAX);
> +
>   	return true;
>   }
>   
> @@ -127,7 +138,7 @@ enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb, bool set_ghcb_msr,
>   				   u64 exit_info_1, u64 exit_info_2)
>   {
>   	/* Fill in protocol and format specifiers */
> -	ghcb->protocol_version = GHCB_PROTOCOL_MAX;
> +	ghcb->protocol_version = ghcb_version;
>   	ghcb->ghcb_usage       = GHCB_DEFAULT_USAGE;
>   
>   	ghcb_set_sw_exit_code(ghcb, exit_code);
>