From: Marc Zyngier Date: Sat, 21 Mar 2026 21:24:16 +0000 (+0000) Subject: KVM: arm64: pkvm: Simplify BTI handling on CPU boot X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1536a0b1386850b67a9ea840e57b7b475e895fed;p=thirdparty%2Fkernel%2Fstable.git KVM: arm64: pkvm: Simplify BTI handling on CPU boot In order to perform an indirect branch to kvm_host_psci_cpu_entry() on a BTI-aware system, we first branch to a 'BTI j' landing pad, and from there branch again to the target. While this works, this is really not required: - BLR works with 'BTI c' and 'PACIASP' as the landing pad - Even if LR gets clobbered by BLR, we are going to restore the host's registers, so it is pointless to try and avoid touching LR Given the above, drop the veneer and directly call into C code. If we were to come back from it, we'd directly enter the error handler. Reviewed-by: Fuad Tabba Tested-by: Fuad Tabba Link: https://patch.msgid.link/20260321212419.2803972-3-maz@kernel.org Signed-off-by: Marc Zyngier --- diff --git a/arch/arm64/kvm/hyp/nvhe/host.S b/arch/arm64/kvm/hyp/nvhe/host.S index eef15b374abb..465f6f1dd641 100644 --- a/arch/arm64/kvm/hyp/nvhe/host.S +++ b/arch/arm64/kvm/hyp/nvhe/host.S @@ -291,13 +291,3 @@ SYM_CODE_START(__kvm_hyp_host_forward_smc) ret SYM_CODE_END(__kvm_hyp_host_forward_smc) - -/* - * kvm_host_psci_cpu_entry is called through br instruction, which requires - * bti j instruction as compilers (gcc and llvm) doesn't insert bti j for external - * functions, but bti c instead. - */ -SYM_CODE_START(kvm_host_psci_cpu_entry) - bti j - b __kvm_host_psci_cpu_entry -SYM_CODE_END(kvm_host_psci_cpu_entry) diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-init.S b/arch/arm64/kvm/hyp/nvhe/hyp-init.S index 5d00bde09201..55e0dce65dc5 100644 --- a/arch/arm64/kvm/hyp/nvhe/hyp-init.S +++ b/arch/arm64/kvm/hyp/nvhe/hyp-init.S @@ -213,12 +213,13 @@ SYM_CODE_START_LOCAL(__kvm_hyp_init_cpu) mov x0, x28 bl ___kvm_hyp_init // Clobbers x0..x2 - /* Leave idmap. */ + /* Leave idmap -- using BLR is OK, LR is restored from host context */ mov x0, x29 - ldr x1, =kvm_host_psci_cpu_entry - br x1 + ldr x1, =__kvm_host_psci_cpu_entry + blr x1 - // The core booted in EL1. KVM cannot be initialized on it. + // The core booted in EL1, or the C code unexpectedly returned. + // Either way, KVM cannot be initialized on it. 1: wfe wfi b 1b