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: Fri, 12 Jan 2024 12:00:01 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Michael Roth <michael.roth@....com>, x86@...nel.org
Cc: 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,
 bp@...en8.de, 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 12/30/23 08:19, 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, that will also lead to a page-fault exception.

I thought we agreed long ago to just demote the whole direct map to 4k
on kernels that might need to act as SEV-SNP hosts.  That should be step
one and this can be discussed as an optimization later.