Re: [PATCH Part1 RFC v3 03/22] x86/sev: Save the negotiated GHCB version

Venu Busireddy
2021-06-08T17:36:36Z

On 2021-06-02 09:03:57 -0500, 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>

Reviewed-by: Venu Busireddy <venu.busireddy@oracle.com>

> ---
> arch/x86/include/asm/sev.h | 2 +-
> arch/x86/kernel/sev-shared.c | 15 ++++++++++++---
> 2 files changed, 13 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> index fa5cd05d3b5b..7ec91b1359df 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 de0e7e6c52b8..70f181f20d92 100644
> --- a/arch/x86/kernel/sev-shared.c
> +++ b/arch/x86/kernel/sev-shared.c
> @@ -14,6 +14,13 @@
> #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.
> + */
> +static u16 ghcb_version __section(".data");
> +
> static bool __init sev_es_check_cpu_features(void)
> {
> if (!has_cpuflag(X86_FEATURE_RDRAND)) {
> @@ -54,10 +61,12 @@ 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;
> }
>
> @@ -101,7 +110,7 @@ static enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb,
> enum es_result ret;
>
> /* 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);
> --
> 2.17.1
>