linux-kernel - Re: [PATCH v2 0/3] Fix several bugs in KVM stage 2 translation

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Message-ID: <20201201205948.GA28178@willie-the-truck>
Date:   Tue, 1 Dec 2020 20:59:48 +0000
From:   Will Deacon <will@...nel.org>
To:     Yanan Wang <wangyanan55@...wei.com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Marc Zyngier <maz@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Gavin Shan <gshan@...hat.com>,
        Quentin Perret <qperret@...gle.com>,
        wanghaibin.wang@...wei.com, yezengruan@...wei.com,
        zhukeqian1@...wei.com, yuzenghui@...wei.com,
        jiangkunkun@...wei.com, wangjingyi11@...wei.com,
        lushenming@...wei.com
Subject: Re: [PATCH v2 0/3] Fix several bugs in KVM stage 2 translation

On Wed, Dec 02, 2020 at 04:10:31AM +0800, Yanan Wang wrote:
> When installing a new pte entry or updating an old valid entry in stage 2
> translation, we use get_page()/put_page() to record page_count of the page-table
> pages. PATCH 1/3 aims to fix incorrect use of get_page()/put_page() in stage 2,
> which might make page-table pages unable to be freed when unmapping a range.
> 
> When dirty logging of a guest with hugepages is finished, we should merge tables
> back into a block entry if adjustment of huge mapping is found necessary.
> In addition to installing the block entry, we should not only free the non-huge
> page-table pages but also invalidate all the TLB entries of non-huge mappings for
> the block. PATCH 2/3 adds enough TLBI when merging tables into a block entry.
> 
> The rewrite of page-table code and fault handling add two different handlers
> for "just relaxing permissions" and "map by stage2 page-table walk", that's
> good improvement. Yet, in function user_mem_abort(), conditions where we choose
> the above two fault handlers are not strictly distinguished. This will causes
> guest errors such as infinite-loop (soft lockup will occur in result), because of
> calling the inappropriate fault handler. So, a solution that can strictly
> distinguish conditions is introduced in PATCH 3/3.

For the series:

Acked-by: Will Deacon <will@...nel.org>

Thanks for reporting these, helping me to understand the issues and then
spinning a v2 so promptly.

Will