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 14C62C9833E for ; Mon, 28 Sep 2026 10:38:18 +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=s3/ye+lygPoBHP6HwfZOQQZUk2Mkc9QfMJk1wsA8Uug=; b=2IIYOaSZMI4YNyjW8wWtoD8jKb 3l86XjRbwMxBsogDlRDWDrNL34PYugRJKr8NC6fxrlbMffxbwhb8EzzzRnfC9uif/4oN8ICzHreQy BecEUDYHcDsTSgaN51APv34XDvXM9ZJFeoeZujP5mR0elu77NfLfB0djsIPzXNODs3y7yuUj1rNOA ONyDzrUGpzcYSlMqmj+f2xDIx2OOXXq320R1rd6EBGU6V8u+5UaMW5r7jNMhc4XAUjOqDk41E8fVC L3zxQkC/3Qbo3NGro4StNO4oSv6seR0QOypzjO/qRfMYu/4lXrytD/kAXXipHfRfiTksYDQnEKyDZ CaQR9Hvw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1xB8kL-00000000MTx-2AAK; Mon, 28 Sep 2026 10:38:09 +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 1xB8kJ-00000000MTH-0s0d for linux-arm-kernel@lists.infradead.org; Mon, 28 Sep 2026 10:38:08 +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 3F45B1595; Mon, 28 Sep 2026 03:38:02 -0700 (PDT) Received: from [10.57.12.79] (unknown [10.57.12.79]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B3BF63F86F; Mon, 28 Sep 2026 03:38:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1790591885; bh=WyhGkEh/Tg98781MkrRtXVLM7OrY9RABxic2LWuUJO0=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=b6e/9zz0pkhgc+qaHVauwUb4u5rmxdp7i1PHyPSXEKggwpo+VB31jvoLg5zQzb/0h iYZ2vFcYs8WFv8M1rrY3QbDiNBuzgTBgfDKeybi4RgMK7SqwG6zIb3YB44LK0PhEqB 4caPUYWw3Z88gErdYPNWuklLnK9KYYIs0cpyhB4c= Message-ID: <3934b4c9-6b1f-44fa-847e-4fb1e67a58e7@arm.com> Date: Mon, 28 Sep 2026 11:38:01 +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> 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-20260928_033807_361024_C7D442F4 X-CRM114-Status: GOOD ( 29.58 ) 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 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 ? And the userspace wouldn't have a mapping for them anyways ? > faults. Kdump is another point raised here: True. > > 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. > > For kdump, we have /proc/vmcore that may be mmap'ed or read() syscalls. > I think Alper proposed an idea to use copy_from_kernel_nofault() (with > exception recovery in do_gpf()) but we'd still need to block > mmap_vmcore() or somehow handle SIGBUS in makedumpfile unless it does > this already. There is a --no-mmap option for makedumpfile in the worst case. > > So, I think we should revisit the GPF handling. If we manage to unmap > all delegated pages, we could limit the exception handling to > is_kdump_kernel(). Otherwise we keep the exception handling as proposed > earlier, maybe with some warnings like EL0 access. Agree. We definitely need this for kdump handling. Suzuki