From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id CC7345111AB; Tue, 29 Sep 2026 10:30:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790677887; cv=none; b=I2ytEKQhi90G5Y6sa6+SbruUydPj28/YEo7Q7grx8ja40DCopSe6Tfd5vS/N7NML23usZtTVynmnTpdMXNWtxiW4QPK3Q1Hp8fHoyOuZt6d33XZj87eC0vXCnGtIiasCAZuinhrnHqU/uZ9yv80r/ZSvPyoKVR1TtJL1LpeK6BY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790677887; c=relaxed/simple; bh=bbdhp9RZEsefco1R5gH5jLRUViZzbWUqmj9Bx9zoiTc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=gyoqFlf/eHOpVKEMcxQu33eVfzejP04XYgMncXd4UvlOdzjYM2jR0GM+KvruO7NV4eSKmGJp1pau/S8ToCzhoptsTGnHWI3pF3zAbSWnEG2c96RYbCv1caJgODgP/ScHedFOWiHPyByvXzeJcU0oBOesVxfWyqcER/EIxQqF3Kk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=MLBHJe93; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="MLBHJe93" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id CB946497; Tue, 29 Sep 2026 03:30:46 -0700 (PDT) Received: from arm.com (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 271D63F86F; Tue, 29 Sep 2026 03:30:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1790677850; bh=bbdhp9RZEsefco1R5gH5jLRUViZzbWUqmj9Bx9zoiTc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=MLBHJe93XO2/suJRTcJpd3d4VEm0QBv3ll9AmKrC3PLu63rQA+ZjIfvlmGw0l4Fg/ pn3iR6FRBOK0ZZVq/LUXYds0tfwqvFJSZjbEJg0Mtj/plMhkNfHCl4NB87iBvhgMYP n2YEYlSP+47rcFYeJ5VCkKHGP9+6+xkTR/GwyuXk= Date: Tue, 29 Sep 2026 11:30:36 +0100 From: Catalin Marinas To: Suzuki K Poulose Cc: Will Deacon , kvm@vger.kernel.org, kvmarm@lists.linux.dev, maz@kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, steven.price@arm.com, aneesh.kumar@kernel.org, oupton@kernel.org, gshan@redhat.com, joey.gouly@arm.com, tabba@google.com, yuzenghui@huawei.com, linux-coco@lists.linux.dev, gankulkarni@os.amperecomputing.com, sdonthineni@nvidia.com, alpergun@google.com, fj0570is@fujitsu.com, WeiLin.Chang@arm.com, lpieralisi@kernel.org, enju.kohei@fujitsu.com Subject: Re: [PATCH v18] arm64: mm: Handle Granule Protection Faults (GPFs) Message-ID: References: <20260913070459.2547407-1-suzuki.poulose@arm.com> <49dcab27-1d03-4df2-b7cb-4df4eda6d909@arm.com> <3934b4c9-6b1f-44fa-847e-4fb1e67a58e7@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3934b4c9-6b1f-44fa-847e-4fb1e67a58e7@arm.com> On Mon, Sep 28, 2026 at 11:38:01AM +0100, Suzuki K Poulose wrote: > On 25/09/2026 18:07, Catalin Marinas wrote: > > On Wed, Sep 23, 2026 at 05:04:06PM +0100, Suzuki K Poulose wrote: > > > On 23/09/2026 16:45, Will Deacon wrote: > > > > On Wed, Sep 23, 2026 at 12:06:15PM +0100, Catalin Marinas wrote: > > > > > On Tue, Sep 22, 2026 at 06:15:34PM +0100, Will Deacon wrote: > > > > > > On Sun, Sep 13, 2026 at 08:04:58AM +0100, Suzuki K Poulose wrote: > > > > > > > From: Steven Price > > > > > > > > > > > > > > If the host attempts to access granules that have been delegated for use > > > > > > > in a realm these accesses will be caught and will trigger a Granule > > > > > > > Protection Fault (GPF). > > > > > > > > > > > > > > A fault during a page walk signals a bug in the kernel and is handled by > > > > > > > oopsing the kernel. A non-page walk fault could be caused by user space > > > > > > > having access to a page which has been delegated to the kernel and will > > > > > > > trigger a SIGBUS to allow debugging why user space is trying to access a > > > > > > > delegated page. > > > > > > > > > > > > > > There is work in progress to unmap the guest_memfd backed private pages from the > > > > > > > linear map. Until we get that support, we could get spurious GPFs from within > > > > > > > the kernel, e.g., load_unaligned_zeropad(). So, try to fix them up for now. > > > > > > > > > > > > > > Reviewed-by: Suzuki K Poulose > > > > > > > Reviewed-by: Gavin Shan > > > > > > > Reviewed-by: Catalin Marinas > > > > > > > Signed-off-by: Steven Price > > > > > > > Signed-off-by: Suzuki K Poulose > > > > > > > --- > > > > > > > Changes since v17: > > > > > > > * Pass untagged address to die_kernel_fault() - Sashiko > > > > > > > * Explicitly check !user_mode() for fixups - Catalin > > > > > > > * Switch to BUS_OBJERR for si_code from SI_KERNEL - Catalin > > > > > > > * Clarify the commit description about the upcoming work on > > > > > > > unmapping guest_memfd backed pages from linear map > > > > > > > Changes since v16: > > > > > > > * Update the commit description to indicate why we try to fixup GPFs > > > > > > > Changes since v10: > > > > > > > * Don't call arm64_notify_die() in do_gpf() but simply return 1. > > > > > > > Changes since v2: > > > > > > > * Include missing "Granule Protection Fault at level -1" > > > > > > > --- > > > > > > > arch/arm64/mm/fault.c | 30 ++++++++++++++++++++++++------ > > > > > > > 1 file changed, 24 insertions(+), 6 deletions(-) > > > > > > > > > > > > I still don't think we should do this, given that the plan is to unmap > > > > > > the memory from the linear map. If this thing fires, it's a kernel bug > > > > > > and it should be fatal. > > > > > > > > > > If the linear unmapping gets merged first, I agree, no need to handle > > > > > these faults. I haven't followed that series, so no idea where it is at. > > > > > > There doesn't seem to be much progress on that series. Brendan > > > volunteered to resurrect the series, taking over from Nikita [0]. > > > But looks like Brendan is not working on this anymore. Will see > > > if someone is really planning to look at it. > > > > > > [0] https://lore.kernel.org/all/DJJ35VLH2PE5.DFD8OYXEOH97@linux.dev > > > > I just realised that this only solves part of the problem. Normal kernel > > allocations are delegated RMM metadata and they'll also trigger GPF > > Other than Kdump, kernel shouldn't try to touch these metadata pages > unless there is a kernel bug ? Hibernate but we need to reject this as well since there's no way you can save and restore the realm memory. > And the userspace wouldn't have a mapping for them anyways ? That's the aim but proposed KVM/CCA support still allows non-gmem slots to end up delegated (I haven't checked the latest if addressed). > > https://lore.kernel.org/all/a11aba04-eaaa-43fd-988b-a2581b1b2fdb@arm.com/ > > > > I think rmi_delegate_range() covers the non-kdump cases, both for > > metadata and realm memory, we could unmap the linear map there (map it > > back in rmi_undelegate_range()). > > We could explore that option for the kernel allocations too. I do wonder what we gain from unmapping. If architecturally we get a synchronous fault when accessing delegated pages, it's only marginally more code to do_gpf() (and we might need this function anyway for kdump) and we avoid linear map fragmentation. So, I think we just need to agree what's fatal and what can safely recover. We do need Alper's patch for kdump, otherwise we can't fix it up in do_gpf(). -- Catalin