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charset=us-ascii Content-Disposition: inline In-Reply-To: <3934b4c9-6b1f-44fa-847e-4fb1e67a58e7@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260929_113054_133434_5998B881 X-CRM114-Status: GOOD ( 48.05 ) 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 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