linux-kernel - Re: [PATCH v1 11/26] x86/sev: Invalidate pages from the direct map when adding them to the RMP table

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Date: Mon, 15 Jan 2024 10:01:26 +0100
From: Borislav Petkov <bp@...en8.de>
To: Michael Roth <michael.roth@....com>
Cc: x86@...nel.org, kvm@...r.kernel.org, linux-coco@...ts.linux.dev,
	linux-mm@...ck.org, linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
	jroedel@...e.de, thomas.lendacky@....com, hpa@...or.com,
	ardb@...nel.org, pbonzini@...hat.com, seanjc@...gle.com,
	vkuznets@...hat.com, jmattson@...gle.com, luto@...nel.org,
	dave.hansen@...ux.intel.com, slp@...hat.com, pgonda@...gle.com,
	peterz@...radead.org, srinivas.pandruvada@...ux.intel.com,
	rientjes@...gle.com, tobin@....com, vbabka@...e.cz,
	kirill@...temov.name, ak@...ux.intel.com, tony.luck@...el.com,
	sathyanarayanan.kuppuswamy@...ux.intel.com, alpergun@...gle.com,
	jarkko@...nel.org, ashish.kalra@....com, nikunj.dadhania@....com,
	pankaj.gupta@....com, liam.merwick@...cle.com, zhi.a.wang@...el.com,
	Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH v1 11/26] x86/sev: Invalidate pages from the direct map
 when adding them to the RMP table

On Sat, Dec 30, 2023 at 10:19:39AM -0600, Michael Roth wrote:
> +	/*
> +	 * If the kernel uses a 2MB directmap mapping to write to an address,
> +	 * and that 2MB range happens to contain a 4KB page that set to private
> +	 * in the RMP table, an RMP #PF will trigger and cause a host crash.

Also:

diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
index 7d294d1a620b..2ad83e7fb2da 100644
--- a/arch/x86/virt/svm/sev.c
+++ b/arch/x86/virt/svm/sev.c
@@ -415,8 +415,9 @@ static int rmpupdate(u64 pfn, struct rmp_state *state)
 
 	/*
 	 * If the kernel uses a 2MB directmap mapping to write to an address,
-	 * and that 2MB range happens to contain a 4KB page that set to private
-	 * in the RMP table, an RMP #PF will trigger and cause a host crash.
+	 * and that 2MB range happens to contain a 4KB page that has been set
+	 * to private in the RMP table, an RMP #PF will trigger and cause a
+	 * host crash.
 	 *
 	 * Prevent this by removing pages from the directmap prior to setting
 	 * them as private in the RMP table.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette