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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 05 Sep 2025 15:45:45.4370 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 8416a9a2-f256-4994-0431-08ddec934734 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: AM4PEPF00027A67.eurprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DB8PR08MB5356 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250905_084556_778559_FF86521E X-CRM114-Status: GOOD ( 21.37 ) 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 This series looks good to me. Reviewed-by: Yeoreum Yun > From: Ard Biesheuvel > > The arm64 port permits the use of the baseline FP/SIMD register file in > kernel mode, and no longer requires preemption to be disabled. Now that > the EFI spec is being clarified to state that EFI runtime services may > only use baseline FP/SIMD, the fact that EFI may code may use FP/SIMD > registers (while executing at the same privilege level as the kernel) is > no longer a reason to disable preemption when invoking them. > > This means that the only remaining reason for disabling preemption is > the fact that the active mm is swapped out and replaced with efi_mm in a > way that is hidden from the scheduler, and so scheduling is not > supported currently. However, given that virtually all (*) EFI runtime > calls are made from the efi_rts_wq workqueue, the efi_mm can simply be > loaded into the workqueue worker kthread while the call is in progress, > and this does not require preemption to be disabled. > > Note that this is only a partial solution in terms of RT guarantees, > given that the runtime services execute at the same privilege level as > the kernel, and can therefore disable interrupts (and therefore > preemption) directly. But it should prevent scheduling latency spikes > for EFI calls that simply take a long time to run to completion. > > Changes since v1/RFC: > - Disable uaccess for SWPAN before updating the preserved TTBR0 value > - Document why disabling migration is needed > - Rebase onto v6.17-rc1 > > (*) only efi_reset_system() and EFI pstore invoke EFI runtime services > without going through the workqueue, and the latter only when saving > a kernel oops log to the EFI varstore > > Cc: Will Deacon > Cc: Mark Rutland > Cc: Sebastian Andrzej Siewior > Cc: Peter Zijlstra > > Ard Biesheuvel (7): > efi: Add missing static initializer for efi_mm::cpus_allowed_lock > efi/runtime: Return success/failure from arch_efi_call_virt_setup() > efi/runtime: Deal with arch_efi_call_virt_setup() returning failure > arm64/fpsimd: Don't warn when EFI execution context is preemptible > arm64/efi: Use a semaphore to protect the EFI stack and FP/SIMD state > arm64/efi: Move uaccess en/disable out of efi_set_pgd() > arm64/efi: Call EFI runtime services without disabling preemption > > arch/arm/include/asm/efi.h | 2 +- > arch/arm64/include/asm/efi.h | 15 ++---- > arch/arm64/kernel/efi.c | 57 +++++++++++++++++--- > arch/arm64/kernel/fpsimd.c | 4 +- > arch/loongarch/include/asm/efi.h | 2 +- > arch/riscv/include/asm/efi.h | 2 +- > arch/x86/include/asm/efi.h | 2 +- > arch/x86/platform/efi/efi_32.c | 3 +- > arch/x86/platform/efi/efi_64.c | 3 +- > arch/x86/platform/uv/bios_uv.c | 3 +- > drivers/firmware/efi/efi.c | 3 ++ > drivers/firmware/efi/riscv-runtime.c | 3 +- > drivers/firmware/efi/runtime-wrappers.c | 20 ++++--- > include/linux/efi.h | 8 +-- > 14 files changed, 89 insertions(+), 38 deletions(-) > > > base-commit: 8f5ae30d69d7543eee0d70083daf4de8fe15d585 > -- > 2.51.0.355.g5224444f11-goog > > -- Sincerely, Yeoreum Yun