From cb87aada970c68c1a210ed68a4a1ce238623e3c3 Mon Sep 17 00:00:00 2001 From: Jessica Clarke Date: Wed, 6 Nov 2024 16:38:17 +0000 Subject: ArmPlatformPkg: Honour RES1 fields in CPTR_EL2 Unlike CPACR_EL1 whose reserved bits are solely RES0, CPTR_EL2 has some RES1 bits, and so we should not clear them unless we know what they mean. For example, when SVE was introduced, CPACR_EL1.ZEN occupied a RES0 field and thus 0 means trap (which is what we get at EL1), but CPTR_EL2.TZ occupied a RES1 field and thus 1 means trap, but we set it to 0, so the environment is inconsistent between EDK2 and EL1 and EL2. Another concrete case is for Morello, where the CEN/TC fields similarly gate access to capability register state, but also alter exception delivery and return, such that VBAR_ELx and ELR_ELx become capabilities. So long as software adheres to RES0/1 this is backwards-compatible, but since EDK2 does not do so here it inadvertently enables capability-based exception delivery and return and thus, when run at EL2, gets stuck in a trap loop when taking its first interrupt, but works just fine at EL1. Fix this by setting all the RES1 fields in CPTR_EL2, following the pattern for CPACR_EL1's non-zero initial value (due to setting FPEN so as to not trap on SIMD/FP use), tested by running ArmVirtQemu-AARCH64 (DEBUG) on Morello QEMU with EL2 enabled. Signed-off-by: Jessica Clarke --- ArmPlatformPkg/Sec/AArch64/Helper.S | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/ArmPlatformPkg/Sec/AArch64/Helper.S b/ArmPlatformPkg/Sec/AArch64/Helper.S index 578c41e0bb..6eebdc41c0 100644 --- a/ArmPlatformPkg/Sec/AArch64/Helper.S +++ b/ArmPlatformPkg/Sec/AArch64/Helper.S @@ -30,7 +30,8 @@ ASM_FUNC(SetupExceptionLevel2) // NB: We assume that we have not been entered on VHE systems with // HCR_EL2.E2H set. - msr cptr_el2, xzr // Enable architectural features + mov x0, #AARCH64_CPTR_DEFAULT + msr cptr_el2, x0 // Enable architectural features // Enable Timer access for non-secure EL1 and EL0 // The cnthctl_el2 register bits are architecturally -- cgit