linux-kernel - Re: [PATCH Part1 RFC v2 09/20] x86/sev: check SEV-SNP features support

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Message-ID: <YKaIDAHOz4+soLxi@zn.tnic>
Date:   Thu, 20 May 2021 18:02:20 +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 09/20] x86/sev: check SEV-SNP features
 support

On Fri, Apr 30, 2021 at 07:16:05AM -0500, Brijesh Singh wrote:
> diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
> index 6d9055427f37..7badbeb6cb95 100644
> --- a/arch/x86/boot/compressed/sev.c
> +++ b/arch/x86/boot/compressed/sev.c
> @@ -25,6 +25,8 @@
>  
>  struct ghcb boot_ghcb_page __aligned(PAGE_SIZE);
>  struct ghcb *boot_ghcb;
> +static u64 sev_status_val;

msr_sev_status should be more descriptive.

> +static bool sev_status_checked;

You don't need this one - you can simply do

	if (!msr_sev_status)
		read the MSR.

>  /*
>   * Copy a version of this function here - insn-eval.c can't be used in
> @@ -119,11 +121,30 @@ static enum es_result vc_read_mem(struct es_em_ctxt *ctxt,
>  /* Include code for early handlers */
>  #include "../../kernel/sev-shared.c"
>  
> +static inline bool sev_snp_enabled(void)
> +{
> +	unsigned long low, high;
> +
> +	if (!sev_status_checked) {
> +		asm volatile("rdmsr\n"
> +			     : "=a" (low), "=d" (high)
> +			     : "c" (MSR_AMD64_SEV));
> +		sev_status_val = (high << 32) | low;
> +		sev_status_checked = true;
> +	}
> +
> +	return sev_status_val & MSR_AMD64_SEV_SNP_ENABLED ? true : false;

	return msr_sev_status & MSR_AMD64_SEV_SNP_ENABLED;

is enough.

> +}
> +
>  static bool early_setup_sev_es(void)
>  {
>  	if (!sev_es_negotiate_protocol())
>  		sev_es_terminate(0, GHCB_SEV_ES_REASON_PROTOCOL_UNSUPPORTED);
>  
> +	/* If SEV-SNP is enabled then check if the hypervisor supports the SEV-SNP features. */

80 cols like the rest of this file pls.

> +	if (sev_snp_enabled() && !sev_snp_check_hypervisor_features())
> +		sev_es_terminate(0, GHCB_SEV_ES_REASON_SNP_UNSUPPORTED);
> +
>  	if (set_page_decrypted((unsigned long)&boot_ghcb_page))
>  		return false;

Thx.

-- 
Regards/Gruss,
    Boris.

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