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 476A2C98321 for ; Fri, 25 Sep 2026 17:07:26 +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:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=NdOVtv43CHf2CxrpTi7sdO3zswv8R0WYHoLKnoRI4Uk=; b=ScEhP2o2JAmDgixc7ub5Xvg/VD C5sw5N5QDy0hHk4QahKz9GnWp259lIDrP/SeMJaOn6FURxGJfhBqZn/kSRY48iGRkm4ZD9kko2STU 45lWArzkF4Xm15ORgEIaxJiaoBpTwZ0/Wq0WGq3VyxKwfLvTW5XZSCb238rgA8tD7Aq8w67PxbGUW faGpKJchosFl9tYBVZUKM0YRPde9ZW2EJO+2VoAX3paepu6dYjylGaDoMDEwlDMHUZSbbgMcIy/YZ p/KyeEYDfS2rMPdzuFXpL6DiqrWxyli/e+PQWoiL+rx8YPhiRTYwwQoD+TWFeKsF0qCVKxWhXTxM4 nIF9GApQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1xA9OJ-0000000E2Tv-1aUk; Fri, 25 Sep 2026 17:07:19 +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 1xA9OG-0000000E2Sy-1nnD for linux-arm-kernel@lists.infradead.org; Fri, 25 Sep 2026 17:07:17 +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 0B9EF169C; Fri, 25 Sep 2026 10:07:11 -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 6F93D3F86F; Fri, 25 Sep 2026 10:07:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1790356034; bh=ixzfrU8lMEsDTomOcbMGSENbu/A9XPEY12QX9G9g3I0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=EHpt1dnkgmEtCXRicfI03eywssdpZdbGJitm2LyU3/txbYynDGJW9GXrNQawbZEyw 3QDLIL1w9E0vjFWl3xfYaRKn3caSX1J1hyvAayOZ7OCj9NKUhHV57vPR+0QirXYeeJ MOzJAeppFl24SLREnFIB5jWlehs2ggbnYJhv2Z8s= Date: Fri, 25 Sep 2026 18:07:08 +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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <49dcab27-1d03-4df2-b7cb-4df4eda6d909@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260925_100716_593002_B1C3BC40 X-CRM114-Status: GOOD ( 36.93 ) 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 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 faults. Kdump is another point raised here: 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()). 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. 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. -- Catalin