linux-kernel - Re: [PATCH v5 05/16] x86/cpu: Defer CR pinning setup until after EFI initialization

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Message-ID: <869c1545-8c94-4820-a861-fbc563056597@intel.com>
Date: Tue, 29 Oct 2024 16:03:37 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: "Luck, Tony" <tony.luck@...el.com>, "Mehta, Sohil"
 <sohil.mehta@...el.com>,
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Subject: Re: [PATCH v5 05/16] x86/cpu: Defer CR pinning setup until after EFI
 initialization

On 10/29/24 15:59, Luck, Tony wrote:
>> *IF* we switched things to do text poking in the upper half of the
>> address space, we'd probably want to find a completely unused PGD entry.
>>  I'm not sure off the top of my head if we have a good one for that or
>> if it's worth the trouble.
> I expect that would be easy on 64-bit (no way the kernel needs all the
> PGD entries from 256..511) but hard for 32-bit (where kernel address
> space is in critically short supply on any machine with >1GB RAM).

Yeah, I was talking about 64-bit only.  On 32-bit PAE a PGD maps 1/4 of
the address space which is totally unworkable for stealing.