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Date: Mon, 15 Jan 2024 10:23:18 +0100
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Subject: Re: [PATCH v1 11/26] x86/sev: Invalidate pages from the direct map
 when adding them to the RMP table
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To: Dave Hansen <dave.hansen@intel.com>,
 Tom Lendacky <thomas.lendacky@amd.com>, Borislav Petkov <bp@alien8.de>
Cc: Michael Roth <michael.roth@amd.com>, x86@kernel.org, kvm@vger.kernel.org,
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From: Vlastimil Babka <vbabka@suse.cz>
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On 1/12/24 21:37, Dave Hansen wrote:
> On 1/12/24 12:28, Tom Lendacky wrote:
>> I thought there was also a desire to remove the direct map for any pages
>> assigned to a guest as private, not just the case that the comment says.
>> So updating the comment would probably the best action.
> 
> I'm not sure who desires that.
> 
> It's sloooooooow to remove things from the direct map.  There's almost
> certainly a frequency cutoff where running the whole direct mapping as
> 4k is better than the cost of mapping/unmapping.
> 
> Actually, where _is_ the TLB flushing here?

Hm yeah it seems to be using the _noflush version? Maybe the RMP issues this
avoids are only triggered with actual page tables and a stray outdated TLB
hit doesn't trigger it? Needs documenting though if that's the case.