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

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Message-ID: <aa3dc7dd-8939-4042-9e02-96dd29e45095@zytor.com>
Date: Tue, 29 Oct 2024 16:05:58 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Dave Hansen <dave.hansen@...el.com>, "Luck, Tony" <tony.luck@...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>,
        Peter Zijlstra <peterz@...radead.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Xiongwei Song <xiongwei.song@...driver.com>,
        "Li, Xin3" <xin3.li@...el.com>,
        "Mike Rapoport (IBM)" <rppt@...nel.org>,
        Brijesh Singh <brijesh.singh@....com>,
        Michael Roth <michael.roth@....com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Alexey Kardashevskiy <aik@....com>
Cc: Jonathan Corbet <corbet@....net>, Ingo Molnar <mingo@...nel.org>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
        "Huang, Kai" <kai.huang@...el.com>,
        Sandipan Das <sandipan.das@....com>, Breno Leitao <leitao@...ian.org>,
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        Alexei Starovoitov <ast@...nel.org>, Hou Tao <houtao1@...wei.com>,
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        Vegard Nossum <vegard.nossum@...cle.com>, Kees Cook <kees@...nel.org>,
        Eric Biggers <ebiggers@...gle.com>, Jason Gunthorpe <jgg@...pe.ca>,
        "Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
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        Rasmus Villemoes <linux@...musvillemoes.dk>,
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        Tejun Heo <tj@...nel.org>, Changbin Du <changbin.du@...wei.com>,
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        Geert Uytterhoeven <geert+renesas@...der.be>,
        Namhyung Kim <namhyung@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>
Subject: Re: [PATCH v5 05/16] x86/cpu: Defer CR pinning setup until after EFI
 initialization

On 10/29/24 16:03, Dave Hansen wrote:
> 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.

But it is also not necessary.

	-hpa