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

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Date:   Tue, 8 Jun 2021 12:35:00 -0500
From:   Venu Busireddy <venu.busireddy@...cle.com>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>, tony.luck@...el.com,
        npmccallum@...hat.com
Subject: Re: [PATCH Part1 RFC v3 03/22] x86/sev: Save the negotiated GHCB
 version

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@....com>

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