linux-kernel - Re: [Patch v2] x86/head/64: remove redundant check on level2_kernel_pgt's _PAGE

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Message-ID: <fej5k6ikc3biecm5xadxgwv2pflktpjmvrxjhzmhia4p5kipun@ny3swf6kcqwi>
Date: Thu, 23 May 2024 13:33:28 +0300
From: "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
To: Wei Yang <richard.weiyang@...il.com>
Cc: tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, 
	dave.hansen@...ux.intel.com, x86@...nel.org, linux-kernel@...r.kernel.org, 
	Ingo Molnar <mingo@...nel.org>, Steve Wahl <steve.wahl@....com>
Subject: Re: [Patch v2] x86/head/64: remove redundant check on
 level2_kernel_pgt's _PAGE_PRESENT bit

On Thu, May 23, 2024 at 08:37:52AM +0000, Wei Yang wrote:
> This patch tries to remove a redundant check on kernel code's PMD
> _PAGE_PRESENT attribute before fix up.

Tries? s/This patch tries to r/R/

> Current process looks like this:
> 
>     pmd in [0, _text)
>         unset _PAGE_PRESENT
>     pmd in [_text, _end]
>         if (_PAGE_PRESENT)
>             fix up delta
>     pmd in (_end, 512)
>         unset _PAGE_PRESENT
> 
> Since we have compiled in _PAGE_PRESENT in this page table, it is not
> necessary to check _PAGE_PRESENT again before fixing up delta

level2_kernel_pgt compiled with _PAGE_PRESENT set. The check is
redundant.


-- 
  Kiryl Shutsemau / Kirill A. Shutemov