linux-kernel - Re: [PATCH v14 06/12] swiotlb: Use is_swiotlb_force

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Date:   Wed, 23 Jun 2021 19:37:37 +0100
From:   Will Deacon <will@...nel.org>
To:     Qian Cai <quic_qiancai@...cinc.com>
Cc:     Claire Chang <tientzu@...omium.org>,
        Rob Herring <robh+dt@...nel.org>, mpe@...erman.id.au,
        Joerg Roedel <joro@...tes.org>,
        Frank Rowand <frowand.list@...il.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        boris.ostrovsky@...cle.com, jgross@...e.com,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        heikki.krogerus@...ux.intel.com, thomas.hellstrom@...ux.intel.com,
        peterz@...radead.org, benh@...nel.crashing.org,
        joonas.lahtinen@...ux.intel.com, dri-devel@...ts.freedesktop.org,
        chris@...is-wilson.co.uk, grant.likely@....com, paulus@...ba.org,
        mingo@...nel.org, jxgao@...gle.com, sstabellini@...nel.org,
        Saravana Kannan <saravanak@...gle.com>, xypron.glpk@....de,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        bskeggs@...hat.com, linux-pci@...r.kernel.org,
        xen-devel@...ts.xenproject.org,
        Thierry Reding <treding@...dia.com>,
        intel-gfx@...ts.freedesktop.org, matthew.auld@...el.com,
        linux-devicetree <devicetree@...r.kernel.org>, daniel@...ll.ch,
        airlied@...ux.ie, maarten.lankhorst@...ux.intel.com,
        linuxppc-dev@...ts.ozlabs.org, jani.nikula@...ux.intel.com,
        Nicolas Boichat <drinkcat@...omium.org>,
        rodrigo.vivi@...el.com, bhelgaas@...gle.com,
        Dan Williams <dan.j.williams@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "list@....net:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
        Jim Quinlan <james.quinlan@...adcom.com>,
        thomas.lendacky@....com, Robin Murphy <robin.murphy@....com>,
        bauerman@...ux.ibm.com
Subject: Re: [PATCH v14 06/12] swiotlb: Use is_swiotlb_force_bounce for
 swiotlb data bouncing

On Wed, Jun 23, 2021 at 12:39:29PM -0400, Qian Cai wrote:
> 
> 
> On 6/18/2021 11:40 PM, Claire Chang wrote:
> > Propagate the swiotlb_force into io_tlb_default_mem->force_bounce and
> > use it to determine whether to bounce the data or not. This will be
> > useful later to allow for different pools.
> > 
> > Signed-off-by: Claire Chang <tientzu@...omium.org>
> > Reviewed-by: Christoph Hellwig <hch@....de>
> > Tested-by: Stefano Stabellini <sstabellini@...nel.org>
> > Tested-by: Will Deacon <will@...nel.org>
> > Acked-by: Stefano Stabellini <sstabellini@...nel.org>
> 
> Reverting the rest of the series up to this patch fixed a boot crash with NVMe on today's linux-next.

Hmm, so that makes patch 7 the suspicious one, right?

Looking at that one more closely, it looks like swiotlb_find_slots() takes
'alloc_size + offset' as its 'alloc_size' parameter from
swiotlb_tbl_map_single() and initialises 'mem->slots[i].alloc_size' based
on 'alloc_size + offset', which looks like a change in behaviour from the
old code, which didn't include the offset there.

swiotlb_release_slots() then adds the offset back on afaict, so we end up
accounting for it twice and possibly unmap more than we're supposed to?

Will