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Subject: Re: [PATCH v15 00/23] Generic page walk and ptdump
To:     Qian Cai <cai@lca.pw>
Cc:     Steven Price <steven.price@arm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux-MM <linux-mm@kvack.org>,
        Mark Rutland <Mark.Rutland@arm.com>,
        the arch/x86 maintainers <x86@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        linux-kernel@vger.kernel.org,
        =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Andy Lutomirski <luto@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        James Morse <james.morse@arm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Will Deacon <will@kernel.org>,
        linux-arm-kernel@lists.infradead.org,
        "Liang, Kan" <kan.liang@linux.intel.com>
References: <20191101140942.51554-1-steven.price@arm.com>
 <1572896147.5937.116.camel@lca.pw>
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 <0FA196FD-3FCD-431A-AA3E-21BF00EA07DC@lca.pw>
From:   David Hildenbrand <david@redhat.com>
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Organization: Red Hat GmbH
Message-ID: <9d5f1689-db82-a6da-d51d-08070aa4bad5@redhat.com>
Date:   Wed, 4 Dec 2019 15:56:58 +0100
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Sender: linux-kernel-owner@vger.kernel.org
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On 04.12.19 15:54, Qian Cai wrote:
> 
> 
>> On Dec 3, 2019, at 6:02 AM, David Hildenbrand <david@redhat.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@lca.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.

I agree, this produces too much noise.


-- 
Thanks,

David / dhildenb