linux-kernel - Re: [PATCH Part1 RFC v2 12/20] x86/compressed: Register GHCB memory when SEV-SNP is active

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Date:   Tue, 25 May 2021 12:41:38 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        tglx@...utronix.de, jroedel@...e.de, thomas.lendacky@....com,
        pbonzini@...hat.com, mingo@...hat.com, dave.hansen@...el.com,
        rientjes@...gle.com, seanjc@...gle.com, peterz@...radead.org,
        hpa@...or.com, tony.luck@...el.com
Subject: Re: [PATCH Part1 RFC v2 12/20] x86/compressed: Register GHCB memory
 when SEV-SNP is active

On Fri, Apr 30, 2021 at 07:16:08AM -0500, Brijesh Singh wrote:
> diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
> index 733fca403ae5..7487d4768ef0 100644
> --- a/arch/x86/include/asm/sev-common.h
> +++ b/arch/x86/include/asm/sev-common.h
> @@ -88,6 +88,18 @@
>  #define GHCB_MSR_PSC_RSVD_MASK		0xfffffULL
>  #define GHCB_MSR_PSC_RESP_VAL(val)	((val) >> GHCB_MSR_PSC_ERROR_POS)
>  
> +/* GHCB GPA Register */
> +#define GHCB_MSR_GPA_REG_REQ		0x012
> +#define GHCB_MSR_GPA_REG_VALUE_POS	12
> +#define GHCB_MSR_GPA_REG_VALUE_MASK	0xfffffffffffffULL

GENMASK_ULL

> +#define GHCB_MSR_GPA_REQ_VAL(v)		\
> +		(((v) << GHCB_MSR_GPA_REG_VALUE_POS) | GHCB_MSR_GPA_REG_REQ)
> +
> +#define GHCB_MSR_GPA_REG_RESP		0x013
> +#define GHCB_MSR_GPA_REG_RESP_VAL(v)	((v) >> GHCB_MSR_GPA_REG_VALUE_POS)
> +#define GHCB_MSR_GPA_REG_ERROR		0xfffffffffffffULL
> +#define GHCB_MSR_GPA_INVALID		~0ULL

Ditto.

> +
>  /* SNP Page State Change NAE event */
>  #define VMGEXIT_PSC_MAX_ENTRY		253
>  #define VMGEXIT_PSC_INVALID_HEADER	0x100000001
> diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
> index 085d3d724bc8..140c5bc07fc2 100644
> --- a/arch/x86/kernel/sev-shared.c
> +++ b/arch/x86/kernel/sev-shared.c
> @@ -81,6 +81,22 @@ static bool ghcb_get_hv_features(void)
>  	return true;
>  }
>  
> +static void snp_register_ghcb(unsigned long paddr)
> +{
> +	unsigned long pfn = paddr >> PAGE_SHIFT;
> +	u64 val;
> +
> +	sev_es_wr_ghcb_msr(GHCB_MSR_GPA_REQ_VAL(pfn));
> +	VMGEXIT();
> +
> +	val = sev_es_rd_ghcb_msr();
> +
> +	/* If the response GPA is not ours then abort the guest */
> +	if ((GHCB_RESP_CODE(val) != GHCB_MSR_GPA_REG_RESP) ||
> +	    (GHCB_MSR_GPA_REG_RESP_VAL(val) != pfn))
> +		sev_es_terminate(1, GHCB_TERM_REGISTER);

Nice, special termination reasons which say why the guest terminates,
cool!

:-)

-- 
Regards/Gruss,
    Boris.

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