linux-kernel - Re: AMD boot woe due to "x86/mm: Cleanup pgprot_4k_2_large() and pgprot_large_2

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Message-Id: <2568586B-B1F7-47F9-8B6F-6A4C0E5280A8@lca.pw>
Date:   Wed, 22 Apr 2020 17:32:00 -0400
From:   Qian Cai <cai@....pw>
To:     Christoph Hellwig <hch@....de>
Cc:     Borislav Petkov <bp@...e.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        x86 <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>
Subject: Re: AMD boot woe due to "x86/mm: Cleanup pgprot_4k_2_large() and
 pgprot_large_2_4k()"



> On Apr 22, 2020, at 1:01 PM, Christoph Hellwig <hch@....de> wrote:
> 
> On Wed, Apr 22, 2020 at 11:55:54AM -0400, Qian Cai wrote:
>> Reverted the linux-next commit and its dependency,
>> 
>> a85573f7e741 ("x86/mm: Unexport __cachemode2pte_tbl”)
>> 9e294786c89a (“x86/mm: Cleanup pgprot_4k_2_large() and pgprot_large_2_4k()”)
>> 
>> fixed crashes or hard reset on AMD machines during boot that have been flagged by
>> KASAN in different forms indicating some sort of memory corruption with this config,
> 
> Interesting.  Your config seems to boot fine in my VM until the point
> where the lack of virtio-blk support stops it from mounting the root
> file system.
> 
> Looking at the patch I found one bug, although that should not affect
> your config (it should use the pgprotval_t type), and one difference
> that could affect code generation, although I prefer the new version
> (use of __pgprot vs a local variable + pgprot_val()).
> 
> Two patches attached, can you try them?
> <0001-x86-Use-pgprotval_t-in-protval_4k_2_large-and-pgprot.patch><0002-foo.patch>

This fixed the sucker,

diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index edf9cea4871f..c54d1d0a8e3b 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -708,7 +708,7 @@ int pud_set_huge(pud_t *pud, phys_addr_t addr, pgprot_t prot)
 
        set_pte((pte_t *)pud, pfn_pte(
                (u64)addr >> PAGE_SHIFT,
-               __pgprot(protval_4k_2_large(pgprot_val(prot) | _PAGE_PSE))));
+               __pgprot(protval_4k_2_large(pgprot_val(prot)) | _PAGE_PSE)));
 
        return 1;
 }