From: Kevin Brodsky Date: Thu, 19 Jun 2025 16:00:42 +0000 (+0100) Subject: arm64: signal: Remove ISB when resetting POR_EL0 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1a665a71ef0fb043c6cfafbf6a6cc9cdc2357505;p=thirdparty%2Flinux.git arm64: signal: Remove ISB when resetting POR_EL0 POR_EL0 is set to its most permissive value before setting up the signal frame, to ensure that uaccess succeeds regardless of the signal stack's pkey. We are now tolerant to spurious POE faults. This means that we do not strictly need to issue an ISB after updating POR_EL0, even when followed by uaccess. The question is whether a fault is likely to happen or not if the ISB is omitted; in this case the answer seems to be no. If the regular stack is used, then it should already be accessible. If the alternate signal stack is used, then a special (inaccessible) pkey may be used - the assumption is that this situation is very uncommon. Remove the ISB to speed up the regular path - this should not have any functional impact regardless of the scenario. Signed-off-by: Kevin Brodsky Link: https://lore.kernel.org/r/20250619160042.2499290-3-kevin.brodsky@arm.com Signed-off-by: Catalin Marinas --- diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c index 417140cd399b3..db3f972f8cd97 100644 --- a/arch/arm64/kernel/signal.c +++ b/arch/arm64/kernel/signal.c @@ -95,8 +95,11 @@ static void save_reset_user_access_state(struct user_access_state *ua_state) ua_state->por_el0 = read_sysreg_s(SYS_POR_EL0); write_sysreg_s(por_enable_all, SYS_POR_EL0); - /* Ensure that any subsequent uaccess observes the updated value */ - isb(); + /* + * No ISB required as we can tolerate spurious Overlay faults - + * the fault handler will check again based on the new value + * of POR_EL0. + */ } }