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charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Aug 10, 2026 at 04:44:51PM +0100, Catalin Marinas wrote: > On Mon, Aug 10, 2026 at 03:14:47PM +0100, Will Deacon wrote: > > On Mon, Aug 10, 2026 at 10:08:18AM -0300, Jason Gunthorpe wrote: > > > On Mon, Aug 10, 2026 at 12:46:51PM +0100, Will Deacon wrote: > > > > On Mon, Aug 10, 2026 at 01:37:11PM +0200, Marek Szyprowski wrote: > > > > > On 10.08.2026 12:20, Will Deacon wrote: > > > > > > On Mon, Aug 10, 2026 at 02:59:42PM +0530, Aneesh Kumar K.V wrote: > > > > > >> Marek Szyprowski writes: > > > > > >> > > > > > >>> On 07.08.2026 20:20, Jason Gunthorpe wrote: > > > > > >>>> On Fri, Aug 07, 2026 at 06:13:49PM +0000, Mostafa Saleh wrote: > > > > > >>>>> But the whole thing is best effort anyway, the kernel picks > > > > > >>>>> IO_TLB_DEFAULT_SIZE which does not depend on the system topology or > > > > > >>>>> how many devices or how much DMA they do. > > > > > >>>>> SWIOTLB memory is wasted if unused so we should be careful around > > > > > >>>>> that as it would be the other way around and users would have to > > > > > >>>>> decrease it manually. > > > > > >>>> Yeah, it is why the arch code shouldn't really be sizing it directly, > > > > > >>>> it should be done in common code and, yes, we are probably going to > > > > > >>>> have to do something alot smarter to have the common code better > > > > > >>>> auto-tune this for the CC case.. > > > > > >>> What about the $subject patch? I assume that it is still needed to > > > > > >>> > > > > > >>> restore the behavior that was altered by the "[PATCH v8 00/23] > > > > > >>> > > > > > >>> dma-mapping: Track shared DMA state through direct, pool and swiotlb > > > > > >>> > > > > > >>> paths?" patchset? > > > > > >>> > > > > > >> I would request that we pick this patch to fix the regression described > > > > > >> in https://lore.kernel.org/all/yq5azeyxyfol.fsf@kernel.org/. > > > > > > I really don't think we need it. CCA hardware isn't exactly widespread > > > > > > and the KVM host side patches don't appear close to being merged. > > > > > > > > > > Does this mean that the branch for-next/coco [1] won't go to v7.3-rc1? > > > > > > Let's not make progress on guest support contingent on KVM CCA host > > > side patches please. I expect the CSPs will have VM instance types > > > available based on CCA within quarters, and Linux as a Guest should > > > work in those environments regardless of what KVM is doing. I don't > > > really expect full KVM support for years, frankly, the patchset is > > > massive. Even Intel and AMD don't have full KVM support yet. > > > > To be clear: the only part I'm pushing back on is the realm-specific hack > > to size the SWIOTLB area in arch/arm64/. Even with that hack applied, I > > don't believe a one-size-fits-all value is going to work for everybody, > > so it was really great to see that special-case removed in: > > > > https://lore.kernel.org/all/20260717180442.110954-18-aneesh.kumar@kernel.org/ > > We had Mostafa's patch here: > > https://lore.kernel.org/all/20260603110522.3331819-4-smostafa@google.com/ > > adding the same swiotlb buffer allocation for pKVM guests and realms. Yes, and I think that's bad for pKVM guests which is why I'm happy to see that part removed. > Aneesh's cleanup of SWIOTLB_FORCE inadvertently removed the 'else' > clause and limited_addressing is now always checked, meaning that we get > size limiting irrespective of whether we still need a default swiotlb. Inadvertently, perhaps, but it's got Tested-bys from three different companies on it and I think it's a good change. I don't think we should be special-casing these environments based on some random collection of virtio devices in a testing setup. > Normally I would consider this a regression on top of mainline and > Mostafa's patches rather than a cleanup. However, if the default size of > the bounce buffer was never sufficient for realms, as you said, we may > need something better here anyway, so not worth fixing. > > I can see x86 in mem_encrypt_setup_arch() adjusting the bounce buffer to > 6% of the guest memory. We could make up similar logic for arm64 or we > could just rely on CONFIG_SWIOTLB_DYNAMIC (default off currently for > arm64 I think). As Jason said, this should be done outside the arch code. Will