linux-kernel - Re: [RFC PATCH 1/1] x86/mm/pat: Clear VM_PAT if copy_p4d

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Message-ID: <95fcd42c-cb41-d280-32a4-97708061fe41@huawei.com>
Date:   Thu, 2 Mar 2023 11:47:16 +0800
From:   mawupeng <mawupeng1@...wei.com>
To:     <dave.hansen@...el.com>, <akpm@...ux-foundation.org>,
        <dave.hansen@...ux.intel.com>, <luto@...nel.org>,
        <peterz@...radead.org>
CC:     <mawupeng1@...wei.com>, <linux-kernel@...r.kernel.org>,
        <x86@...nel.org>, <bp@...e.de>, <toshi.kani@...com>,
        <suresh.b.siddha@...el.com>,
        <syzbot+5f488e922d047d8f00cc@...kaller.appspotmail.com>
Subject: Re: [RFC PATCH 1/1] x86/mm/pat: Clear VM_PAT if copy_p4d_range failed



On 2023/2/23 4:03, Dave Hansen wrote:
> On 2/16/23 18:56, Wupeng Ma wrote:
>> dup_mm
>>   dup_mmap
>>     copy_page_range
>>       copy_p4d_range
>>         copy_pud_range
>>           copy_pmd_range
>>             pmd_alloc
>>               __pmd_alloc
>>                 pmd_alloc_one
>>                   page = alloc_pages(gfp, 0);
>>                     if (!page)
>>                       return NULL;
>>     mmput
>>         exit_mmap
>>           unmap_vmas
>>             unmap_single_vma
>>               untrack_pfn
>>                 follow_phys
>>                   WARN_ON_ONCE(1);
> 
> What's the point of that warning in the first place?  I can certainly
> imagine follow_phys() failing for sparse mappings, for instance.  Is
> there some requirement that VM_PFNMAP can't be sparse?

Hi Dave

Thanks for reviewing.

Sorry，I have no idea why warning in the first place.

I think we can delete this WARN_ON_ONCE with another patch?