linux-kernel - Re: [PATCH] mm: Fix PTE_AF handling in fault path on architectures with HW AF support

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Message-ID: <d1ea4228-9ee0-41de-9119-e9a8a577ca51@intel.com>
Date: Wed, 10 Jul 2024 09:08:13 +0800
From: "Yin, Fengwei" <fengwei.yin@...el.com>
To: Ram Tummala <rtummala@...dia.com>, <akpm@...ux-foundation.org>
CC: <willy@...radead.org>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>, <apopple@...dia.com>,
	<stable@...r.kernel.org>
Subject: Re: [PATCH] mm: Fix PTE_AF handling in fault path on architectures
 with HW AF support



On 7/10/2024 8:09 AM, Ram Tummala wrote:
> The polarity of prefault calculation is incorrect. This leads to prefault
> being incorrectly set for the faulting address. The following if check will
> incorrectly clear the PTE_AF bit instead of setting it and the access will
> fault again on the same address due to the missing PTE_AF bit.
> 
>      if (prefault && arch_wants_old_prefaulted_pte())
>          entry = pte_mkold(entry);

I have same confusion as Matthew about the PTE_AF.

But I think this is a good catch as old code is like:
         bool prefault = vmf->address != addr;

Sorry for the issue by me. And

Reviewed-by: Yin Fengwei <fengwei.yin@...el.com>


Regards
Yin, Fengwei