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From: Alexandru Elisei <alexandru.elisei@arm.com>
To: Gavin Shan <gshan@redhat.com>, kvmarm@lists.cs.columbia.edu
Cc: maz@kernel.org, shan.gavin@gmail.com
Subject: Re: [PATCH] arm64/kvm: Fix zapping stage2 page table wrongly
Date: Wed, 2 Sep 2020 11:59:18 +0100	[thread overview]
Message-ID: <dbd37825-9f3b-1911-cba5-03099250dc7e@arm.com> (raw)
In-Reply-To: <20200822024444.28132-1-gshan@redhat.com>

Hi,

On 8/22/20 3:44 AM, Gavin Shan wrote:
> Depending on the kernel configuration, PUD_SIZE could be equal to
> PMD_SIZE. For example, both of them are 512MB with the following
> kernel configuration. In this case, both PUD and PMD are folded
> to PGD.
>
>    CONFIG_ARM64_64K_PAGES   y
>    CONFIG_ARM64_VA_BITS     42
>    CONFIG_PGTABLE_LEVELS    2
>
> With the above configuration, the stage2 PUD is used to backup the
> 512MB huge page when the stage2 mapping is built. During the mapping,
> the PUD and its subordinate levels of page table entries are unmapped
> if the PUD is present and not huge page sensitive in stage2_set_pud_huge().
> Unfornately, the @addr isn't aligned to S2_PUD_SIZE and wrong page table
> entries are zapped. It eventually leads to PUD's present bit can't be
> cleared successfully and infinite loop in stage2_set_pud_huge().
>
> This fixes the issue by checking with S2_{PUD, PMD}_SIZE instead of
> {PUD, PMD}_SIZE to determine if stage2 PUD or PMD is used to back the
> huge page. For this particular case, the stage2 PMD entry should be
> used to backup the 512MB huge page with stage2_set_pmd_huge().

I can reproduce this on my rockpro64 using kvmtool.

I see two issues here: first, PUD_SIZE = 512MB, but S2_PUD_SIZE = 4TB (checked
using printk), and second, stage2_set_pud_huge() hangs. I'm working on debugging them.

Thanks,

Alex

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  parent reply	other threads:[~2020-09-02 10:58 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-22  2:44 [PATCH] arm64/kvm: Fix zapping stage2 page table wrongly Gavin Shan
2020-08-22 10:01 ` Marc Zyngier
2020-08-22 23:59   ` Gavin Shan
2020-09-01 16:50     ` Marc Zyngier
2020-09-02 10:59 ` Alexandru Elisei [this message]
2020-09-02 11:10   ` Marc Zyngier
2020-09-02 11:53     ` Alexandru Elisei
2020-09-02 11:56       ` Alexandru Elisei
2020-09-02 12:04       ` Marc Zyngier
2020-09-02 13:58         ` Alexandru Elisei
2020-09-02 17:38     ` Auger Eric
2020-09-02 23:55     ` Gavin Shan

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