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Mon, 10 Aug 2026 14:33:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786372403; bh=7nq4F6eVa+igOyPizq1W0mha35WNgJ79/K+NijHuU08=; h=From:To:Cc:Subject:In-Reply-To:References:Date; b=FSEg5P7W76NmVIq/uL3ZJ2JQ93MR3s+H6sZ8oMjTjqoQtXHtpU2o8sZMVTuz5+8hg s/icfW+TbRoP+BIL+Loawx2mDkc39Fga6I40bNBiXUw3nB8b264pGFeY2r4EsV+SQ/ Q48Vqv2S8+JWnnwUTV2LAOB1KEzUy1OtCTc2kDiWMYMhfgicWh6aJLxgocxnjXteXp Uh7ToRG+nxYY1VwUX4I2D+iq7cDjxmG7Qmo1ULPbcjMYqklUgFlWSNeJqJLZLC9zWi jGnT9IpWporSvmykehgrhxxupjX8d/mSoeZuCdmoSHpGyNGZ6YcvG7+JV12NxM75p3 1qv9ezVXXbK8w== X-Mailer: emacs 30.2 (via feedmail 11-beta-1 I) From: Aneesh Kumar K.V To: Jason Gunthorpe , Will Deacon Cc: Marek Szyprowski , Mostafa Saleh , iommu@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-coco@lists.linux.dev, Robin Murphy , Marc Zyngier , Steven Price , Suzuki K Poulose , Catalin Marinas , Jiri Pirko , Petr Tesarik , Alexey Kardashevskiy , Dan Williams , Xu Yilun , linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Sven Schnelle , x86@kernel.org Subject: Re: [PATCH] arm64: swiotlb: Keep the default size for protected guests In-Reply-To: <20260810130818.GN200537@ziepe.ca> References: <20260807164734.GE200537@ziepe.ca> <20260807182017.GH200537@ziepe.ca> <7d22482f-d5fd-4cf4-9d32-6a54e02f2fbb@samsung.com> <28442500-1d53-4776-bae5-459c3ffc1cc6@samsung.com> <20260810130818.GN200537@ziepe.ca> Date: Mon, 10 Aug 2026 20:03:09 +0530 Message-ID: X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Jason Gunthorpe writes: > 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 direc= tly, >> > >>>> 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 swiot= lb >> > >>> >> > >>> paths?" patchset? >> > >>> >> > >> I would request that we pick this patch to fix the regression descr= ibed >> > >> in https://lore.kernel.org/all/yq5azeyxyfol.fsf@kernel.org/. >> > > I really don't think we need it. CCA hardware isn't exactly widespre= ad >> > > and the KVM host side patches don't appear close to being merged. >> >=20 >> > Does this mean that the branch for-next/coco [1]=C2=A0won'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. > > People already have CCA capable HW, are already testing this stuff and > the closer upstream can get to being workable as a guest without a > mountain of OOT patches the better. > > I agree the thing is not ideal, but it was merged to ARM like this a > long time ago, this patch is just fixing a small oopsie (was it a > merge conflict?) to put it back. I don't the objection. > It was not a merge conflict issue. The change was introduced by an incorrect rebase I did when updating the patch series on top of the pKVM changes. -aneesh