linux-kernel - Re: [RFC 5/6] Hibernate: Add check for pte

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Message-ID: <YoTwDOot4Ww9JhdS@infradead.org>
Date:   Wed, 18 May 2022 06:09:32 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Vivek Kumar <quic_vivekuma@...cinc.com>
Cc:     corbet@....net, catalin.marinas@....com, will@...nel.org,
        tglx@...utronix.de, maz@...nel.org, axboe@...nel.dk,
        rafael@...nel.org, akpm@...ux-foundation.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-block@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-mm@...ck.org, len.brown@...el.com,
        pavel@....cz, paulmck@...nel.org, bp@...e.de,
        keescook@...omium.org, songmuchun@...edance.com,
        rdunlap@...radead.org, damien.lemoal@...nsource.wdc.com,
        pasha.tatashin@...een.com, tabba@...gle.com, ardb@...nel.org,
        tsoni@...cinc.com, quic_psodagud@...cinc.com,
        quic_svaddagi@...cinc.com,
        Prasanna Kumar <quic_kprasan@...cinc.com>
Subject: Re: [RFC 5/6] Hibernate: Add check for pte_valid in saveable page

On Wed, May 18, 2022 at 01:18:40PM +0530, Vivek Kumar wrote:
> Add check for pte_valid in saveable page after being checked for
> the rest. This is required as PTE is removed for pages allocated
> with dma_alloc_coherent with DMA_ATTR_NO_KERNEL_MAPPING flag set.
> This patch makes sure that these pages are not considered for
> snapshot.

I don't think we ever remove kernel PTEs for DMA_ATTR_NO_KERNEL_MAPPING.
If the allocation did come from highmem they never had one to start
with.  The logic here looks a bit fishy to me.