linux-kernel - Re: [PATCH v15 00/23] Generic page walk and ptdump

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Date:   Wed, 4 Dec 2019 09:54:53 -0500
From:   Qian Cai <cai@....pw>
To:     David Hildenbrand <david@...hat.com>
Cc:     Steven Price <steven.price@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux-MM <linux-mm@...ck.org>,
        Mark Rutland <Mark.Rutland@....com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org,
        Jérôme Glisse <jglisse@...hat.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        James Morse <james.morse@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        "Liang, Kan" <kan.liang@...ux.intel.com>
Subject: Re: [PATCH v15 00/23] Generic page walk and ptdump



> On Dec 3, 2019, at 6:02 AM, David Hildenbrand <david@...hat.com> wrote:
> 
> On 06.11.19 16:05, Steven Price wrote:
>> On 06/11/2019 13:31, Qian Cai wrote:
>>> 
>>> 
>>>> On Nov 4, 2019, at 2:35 PM, Qian Cai <cai@....pw> wrote:
>>>> 
>>>> On Fri, 2019-11-01 at 14:09 +0000, Steven Price wrote:
>> [...]
>>>>> Changes since v14:
>>>>> https://lore.kernel.org/lkml/20191028135910.33253-1-steven.price@arm.com/
>>>>> * Switch walk_page_range() into two functions, the existing
>>>>>   walk_page_range() now still requires VMAs (and treats areas without a
>>>>>   VMA as a 'hole'). The new walk_page_range_novma() ignores VMAs and
>>>>>   will report the actual page table layout. This fixes the previous
>>>>>   breakage of /proc/<pid>/pagemap
>>>>> * New patch at the end of the series which reduces the 'level' numbers
>>>>>   by 1 to simplify the code slightly
>>>>> * Added tags
>>>> 
>>>> Does this new version also take care of this boot crash seen with v14? Suppose
>>>> it is now breaking CONFIG_EFI_PGT_DUMP=y? The full config is,
>>>> 
>>>> https://raw.githubusercontent.com/cailca/linux-mm/master/x86.config
>>>> 
>>> 
>>> V15 is indeed DOA here.
>> 
>> Thanks for finding this, it looks like EFI causes issues here. The below fixes
>> this for me (booting in QEMU).
>> 
>> Andrew: do you want me to send out the entire series again for this fix, or
>> can you squash this into mm-pagewalk-allow-walking-without-vma.patch?
>> 
>> Thanks,
>> 
>> Steve
>> 
>> ---8<---
>> diff --git a/mm/pagewalk.c b/mm/pagewalk.c
>> index c7529dc4f82b..70dcaa23598f 100644
>> --- a/mm/pagewalk.c
>> +++ b/mm/pagewalk.c
>> @@ -90,7 +90,7 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
>>  			split_huge_pmd(walk->vma, pmd, addr);
>>  			if (pmd_trans_unstable(pmd))
>>  				goto again;
>> -		} else if (pmd_leaf(*pmd)) {
>> +		} else if (pmd_leaf(*pmd) || !pmd_present(*pmd)) {
>>  			continue;
>>  		}
>> 
>> @@ -141,7 +141,7 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
>>  			split_huge_pud(walk->vma, pud, addr);
>>  			if (pud_none(*pud))
>>  				goto again;
>> -		} else if (pud_leaf(*pud)) {
>> +		} else if (pud_leaf(*pud) || !pud_present(*pud)) {
>>  			continue;
>>  		}
>> 
>> 
> 
> Even with this fix, booting for me under QEMU fails. See
> 
> https://lore.kernel.org/linux-mm/b7ce62f2-9a48-6e48-6685-003431e521aa@redhat.com/
> 

Yes, for some reasons, this starts to crash on almost all arches here, so it might be worth
for Andrew to revert those in the meantime while allowing Steven to rework.