From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 1377FCA5FA5 for ; Tue, 29 Sep 2026 10:42:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=chjH6PAnr7p+DZMPHLtIyVggq/S3XE3ABXSawW/YmSw=; b=EyjBDogThI2aLQtS96vT4OSm+H dEDOfDbr6Fl5Dd4kf6/T9hzy7Me1iQygUTCbkhI1UHk2Q6ZTq/X+EUItrDWU29yr0u38nYTDoE9yM Rp+aimW6dmDl9xsSuw3CvMs0EOLMevHl6pbnV4dSRXOvWLhvt+1E7IyWzoVycFNytHUSa62iDUDcF hT1MqRgP1eWEgK3YY38X1abjeroMBC4ZQ5HGpMZvI9YNuaE95tLfydN0/DL3bY3E2VFkcb7/70Ehr yC/NTtM7GQg5hNBUj0z7OfZmfvb0Mz2QXrxs+GOIfh63u/cNBjGY/WMAWaStlFbNGwN3OfpnDGjNi mce5dchg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1xBVHr-00000003IiB-3o6B; Tue, 29 Sep 2026 10:42:16 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1xBVHp-00000003Ih2-0A1m for linux-arm-kernel@lists.infradead.org; Tue, 29 Sep 2026 10:42:14 +0000 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 2BA63497; Tue, 29 Sep 2026 03:42:07 -0700 (PDT) Received: from [10.57.12.116] (unknown [10.57.12.116]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A904A3F86F; Tue, 29 Sep 2026 03:42:07 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1790678530; bh=7/qDNxbBp1ADohJnweYVMAso5g2WF/JpQG/PO2h7y30=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=PC0ik/ydlxF//U+lOzOT0FQMQrw91+SgzqjHx8bSSGqPb2dUxJ8O169VPU4eiTqnA fm3nTXkhVLT4Z/MtxA698ns0dQ477LlEA5AfOd7bC58zuZOSRkbEXUw6qxg/8JlVG1 CQlrL5P0hFD8zGPUViyWR8naA+LE5p96UT9StgiU= Message-ID: Date: Tue, 29 Sep 2026 11:42:06 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v18] arm64: mm: Handle Granule Protection Faults (GPFs) Content-Language: en-GB To: Catalin Marinas 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 References: <20260913070459.2547407-1-suzuki.poulose@arm.com> <49dcab27-1d03-4df2-b7cb-4df4eda6d909@arm.com> <3934b4c9-6b1f-44fa-847e-4fb1e67a58e7@arm.com> From: Suzuki K Poulose In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260929_034213_175758_7B75FB12 X-CRM114-Status: GOOD ( 34.04 ) 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 29/09/2026 11:30, Catalin Marinas wrote: > 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. Ack. I have disabled both kexec (including kdump for now, more on that below) and hibernate when RMM is active. > >> 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). This has been addressed in v20 integration branch here : https://git.gitlab.arm.com/linux-arm/linux-cca/-/commit/0e697f0f3b2c11855192ae6e80d6036e9374ccef?file_path=arch%2Farm64%2Fkvm%2Fmmu.c#line_b12897615_A2307 > >>> 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(). Ack. We could add that in later series. For now we block all kexecs. Cheers Suzuki >