linux-kernel - Re: [PATCH Part1 RFC v3 08/22] x86/compressed: Add helper for validating pages in the decompression stage

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Date:   Tue, 8 Jun 2021 13:12:35 +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,
        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 08/22] x86/compressed: Add helper for
 validating pages in the decompression stage

On Wed, Jun 02, 2021 at 09:04:02AM -0500, Brijesh Singh wrote:
> +static void __page_state_change(unsigned long paddr, int op)
> +{
> +	u64 val;
> +
> +	if (!sev_snp_enabled())
> +		return;
> +
> +	/*
> +	 * If private -> shared then invalidate the page before requesting the
> +	 * state change in the RMP table.
> +	 */
> +	if ((op == SNP_PAGE_STATE_SHARED) && pvalidate(paddr, RMP_PG_SIZE_4K, 0))
> +		goto e_pvalidate;
> +
> +	/* Issue VMGEXIT to change the page state in RMP table. */
> +	sev_es_wr_ghcb_msr(GHCB_MSR_PSC_REQ_GFN(paddr >> PAGE_SHIFT, op));
> +	VMGEXIT();
> +
> +	/* Read the response of the VMGEXIT. */
> +	val = sev_es_rd_ghcb_msr();
> +	if ((GHCB_RESP_CODE(val) != GHCB_MSR_PSC_RESP) || GHCB_MSR_PSC_RESP_VAL(val))
> +		sev_es_terminate(1, GHCB_TERM_PSC);
> +
> +	/*
> +	 * Now that page is added in the RMP table, validate it so that it is
> +	 * consistent with the RMP entry.
> +	 */
> +	if ((op == SNP_PAGE_STATE_PRIVATE) && pvalidate(paddr, RMP_PG_SIZE_4K, 1))
> +		goto e_pvalidate;
> +
> +	return;
> +
> +e_pvalidate:
> +	sev_es_terminate(1, GHCB_TERM_PVALIDATE);
> +}

You don't even need that label, diff ontop:

diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index 808fe1f6b170..dd0f22386fd2 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -146,7 +146,7 @@ static void __page_state_change(unsigned long paddr, int op)
 	 * state change in the RMP table.
 	 */
 	if ((op == SNP_PAGE_STATE_SHARED) && pvalidate(paddr, RMP_PG_SIZE_4K, 0))
-		goto e_pvalidate;
+		sev_es_terminate(1, GHCB_TERM_PVALIDATE);
 
 	/* Issue VMGEXIT to change the page state in RMP table. */
 	sev_es_wr_ghcb_msr(GHCB_MSR_PSC_REQ_GFN(paddr >> PAGE_SHIFT, op));
@@ -162,12 +162,7 @@ static void __page_state_change(unsigned long paddr, int op)
 	 * consistent with the RMP entry.
 	 */
 	if ((op == SNP_PAGE_STATE_PRIVATE) && pvalidate(paddr, RMP_PG_SIZE_4K, 1))
-		goto e_pvalidate;
-
-	return;
-
-e_pvalidate:
-	sev_es_terminate(1, GHCB_TERM_PVALIDATE);
+		sev_es_terminate(1, GHCB_TERM_PVALIDATE);
 }
 
 void snp_set_page_private(unsigned long paddr)

-- 
Regards/Gruss,
    Boris.

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