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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Message-ID: <20240112200751.GHZaGcF0-OZVJiIB7y@fat_crate.local>
Date: Fri, 12 Jan 2024 21:07:51 +0100
From: Borislav Petkov <bp@...en8.de>
To: Dave Hansen <dave.hansen@...el.com>
Cc: Michael Roth <michael.roth@....com>, 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,
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	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 Fri, Jan 12, 2024 at 12:00:01PM -0800, Dave Hansen wrote:
> 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.

What would be the disadvantage here? Higher TLB pressure when running
kernel code I guess...

-- 
Regards/Gruss,
    Boris.

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