Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Thu, 8 Jul 2021 17:44:19 +0100
From:   Will Deacon <will@kernel.org>
To:     Nathan Chancellor <nathan@kernel.org>
Cc:     Robin Murphy <robin.murphy@arm.com>,
        Christoph Hellwig <hch@lst.de>,
        heikki.krogerus@linux.intel.com, thomas.hellstrom@linux.intel.com,
        peterz@infradead.org, benh@kernel.crashing.org,
        joonas.lahtinen@linux.intel.com, dri-devel@lists.freedesktop.org,
        chris@chris-wilson.co.uk, grant.likely@arm.com, paulus@samba.org,
        Frank Rowand <frowand.list@gmail.com>, mingo@kernel.org,
        Stefano Stabellini <sstabellini@kernel.org>,
        Saravana Kannan <saravanak@google.com>, mpe@ellerman.id.au,
        "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
        Bartosz Golaszewski <bgolaszewski@baylibre.com>,
        bskeggs@redhat.com, linux-pci@vger.kernel.org,
        xen-devel@lists.xenproject.org,
        Thierry Reding <treding@nvidia.com>,
        intel-gfx@lists.freedesktop.org, matthew.auld@intel.com,
        linux-devicetree <devicetree@vger.kernel.org>,
        Jianxiong Gao <jxgao@google.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        maarten.lankhorst@linux.intel.com, airlied@linux.ie,
        Dan Williams <dan.j.williams@intel.com>,
        linuxppc-dev@lists.ozlabs.org, jani.nikula@linux.intel.com,
        Rob Herring <robh+dt@kernel.org>, rodrigo.vivi@intel.com,
        Bjorn Helgaas <bhelgaas@google.com>,
        Claire Chang <tientzu@chromium.org>,
        boris.ostrovsky@oracle.com,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        jgross@suse.com, Nicolas Boichat <drinkcat@chromium.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        Qian Cai <quic_qiancai@quicinc.com>,
        lkml <linux-kernel@vger.kernel.org>,
        "list@263.net:IOMMU DRIVERS" <iommu@lists.linux-foundation.org>,
        Jim Quinlan <james.quinlan@broadcom.com>, xypron.glpk@gmx.de,
        Tom Lendacky <thomas.lendacky@amd.com>, bauerman@linux.ibm.com
Subject: Re: [PATCH v15 06/12] swiotlb: Use is_swiotlb_force_bounce for
 swiotlb data bouncing
Message-ID: <20210708164418.GB23598@willie-the-truck>
References: <0f7bd903-e309-94a0-21d7-f0e8e9546018@arm.com>
 <YN/7xcxt/XGAKceZ@Ryzen-9-3900X.localdomain>
 <20210705190352.GA19461@willie-the-truck>
 <20210706044848.GA13640@lst.de>
 <20210706132422.GA20327@willie-the-truck>
 <a59f771f-3289-62f0-ca50-8f3675d9b166@arm.com>
 <20210706140513.GA26498@lst.de>
 <bb32d5a6-2b34-4524-e171-3e9f5f4d3a94@arm.com>
 <20210706170657.GD20750@willie-the-truck>
 <e1c026c6-22c7-8979-4941-de9cfab3863a@kernel.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <e1c026c6-22c7-8979-4941-de9cfab3863a@kernel.org>
User-Agent: Mutt/1.10.1 (2018-07-13)
Precedence: bulk

On Tue, Jul 06, 2021 at 12:14:16PM -0700, Nathan Chancellor wrote:
> On 7/6/2021 10:06 AM, Will Deacon wrote:
> > On Tue, Jul 06, 2021 at 04:39:11PM +0100, Robin Murphy wrote:
> > > On 2021-07-06 15:05, Christoph Hellwig wrote:
> > > > On Tue, Jul 06, 2021 at 03:01:04PM +0100, Robin Murphy wrote:
> > > > > FWIW I was pondering the question of whether to do something along those
> > > > > lines or just scrap the default assignment entirely, so since I hadn't got
> > > > > round to saying that I've gone ahead and hacked up the alternative
> > > > > (similarly untested) for comparison :)
> > > > > 
> > > > > TBH I'm still not sure which one I prefer...
> > > > 
> > > > Claire did implement something like your suggestion originally, but
> > > > I don't really like it as it doesn't scale for adding multiple global
> > > > pools, e.g. for the 64-bit addressable one for the various encrypted
> > > > secure guest schemes.
> > > 
> > > Ah yes, that had slipped my mind, and it's a fair point indeed. Since we're
> > > not concerned with a minimal fix for backports anyway I'm more than happy to
> > > focus on Will's approach. Another thing is that that looks to take us a
> > > quiet step closer to the possibility of dynamically resizing a SWIOTLB pool,
> > > which is something that some of the hypervisor protection schemes looking to
> > > build on top of this series may want to explore at some point.
> > 
> > Ok, I'll split that nasty diff I posted up into a reviewable series and we
> > can take it from there.
> 
> For what it's worth, I attempted to boot Will's diff on top of Konrad's
> devel/for-linus-5.14 and it did not work; in fact, I got no output on my
> monitor period, even with earlyprintk=, and I do not think this machine has
> a serial console.

Looking back at the diff, I completely messed up swiotlb_exit() by mixing up
physical and virtual addresses.

> Robin's fix does work, it survived ten reboots with no issues getting to X
> and I do not see the KASAN and slub debug messages anymore but I understand
> that this is not the preferred solution it seems (although Konrad did want
> to know if it works).
> 
> I am happy to test any further patches or follow ups as needed, just keep me
> on CC.

Cheers. Since this isn't 5.14 material any more, I'll CC you on a series
next week.

Will