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

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Message-ID: <ae1ce014-cf09-4e92-8d93-282042975aee@zytor.com>
Date: Tue, 29 Oct 2024 16:02:24 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: "Luck, Tony" <tony.luck@...el.com>,
        "Hansen, Dave"
 <dave.hansen@...el.com>,
        "Mehta, Sohil" <sohil.mehta@...el.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "x86@...nel.org"
 <x86@...nel.org>,
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        "Mike Rapoport (IBM)" <rppt@...nel.org>,
        Brijesh Singh <brijesh.singh@....com>,
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        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
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Cc: Jonathan Corbet <corbet@....net>, Ingo Molnar <mingo@...nel.org>,
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        Daniel Sneddon <daniel.sneddon@...ux.intel.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).

No LASS on 32 bits...

	-hpa