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From:   Steven Price <steven.price@arm.com>
Subject: Re: [PATCH v15 00/23] Generic page walk and ptdump
To:     Qian Cai <cai@lca.pw>, Andrew Morton <akpm@linux-foundation.org>,
        linux-mm@kvack.org
Cc:     Mark Rutland <Mark.Rutland@arm.com>, 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>
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Message-ID: <16da6118-ac4d-a165-6202-0731a776ac72@arm.com>
Date:   Wed, 6 Nov 2019 15:05:29 +0000
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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;
  		}