According to the SMCCC spec[1](7.5.2 Discovery) the ARM_SMCCC_ARCH_WORKAROUND_1 function id only returns 0, 1, and SMCCC_RET_NOT_SUPPORTED. 0 is "workaround required and safe to call this function" 1 is "workaround not required but safe to call this function" SMCCC_RET_NOT_SUPPORTED is "might be vulnerable or might not be, who knows, I give up!" SMCCC_RET_NOT_SUPPORTED might as well mean "workaround required, except calling this function may not work because it isn't implemented in some cases". Wonderful. We map this SMC call to 0 is SPECTRE_MITIGATED 1 is SPECTRE_UNAFFECTED SMCCC_RET_NOT_SUPPORTED is SPECTRE_VULNERABLE For KVM hypercalls (hvc), we've implemented this function id to return SMCCC_RET_NOT_SUPPORTED, 0, and SMCCC_RET_NOT_REQUIRED. One of those isn't supposed to be there. Per the code we call arm64_get_spectre_v2_state() to figure out what to return for this feature discovery call. 0 is SPECTRE_MITIGATED SMCCC_RET_NOT_REQUIRED is SPECTRE_UNAFFECTED SMCCC_RET_NOT_SUPPORTED is SPECTRE_VULNERABLE Let's clean this up so that KVM tells the guest this mapping: 0 is SPECTRE_MITIGATED 1 is SPECTRE_UNAFFECTED SMCCC_RET_NOT_SUPPORTED is SPECTRE_VULNERABLE Note: SMCCC_RET_NOT_AFFECTED is 1 but isn't part of the SMCCC spec Cc: Andre Przywara <andre.przywara@xxxxxxx> Cc: Steven Price <steven.price@xxxxxxx> Cc: Marc Zyngier <maz@xxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Link: https://developer.arm.com/documentation/den0028/latest [1] Fixes: c118bbb52743 ("arm64: KVM: Propagate full Spectre v2 workaround state to KVM guests") Signed-off-by: Stephen Boyd <swboyd@xxxxxxxxxxxx> --- I see that before commit c118bbb52743 ("arm64: KVM: Propagate full Spectre v2 workaround state to KVM guests") we had this mapping: 0 is SPECTRE_MITIGATED SMCCC_RET_NOT_SUPPORTED is SPECTRE_VULNERABLE so the return value '1' wasn't there then. Once the commit was merged we introduced the notion of NOT_REQUIRED here when it shouldn't have been introduced. Changes from v2: * Moved define to header file and used it Changes from v1: * Way longer commit text, more background (sorry) * Dropped proton-pack part because it was wrong * Rebased onto other patch accepted upstream arch/arm64/kernel/proton-pack.c | 2 -- arch/arm64/kvm/hypercalls.c | 2 +- include/linux/arm-smccc.h | 2 ++ 3 files changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/arm64/kernel/proton-pack.c b/arch/arm64/kernel/proton-pack.c index 25f3c80b5ffe..c18eb7d41274 100644 --- a/arch/arm64/kernel/proton-pack.c +++ b/arch/arm64/kernel/proton-pack.c @@ -135,8 +135,6 @@ static enum mitigation_state spectre_v2_get_cpu_hw_mitigation_state(void) return SPECTRE_VULNERABLE; } -#define SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED (1) - static enum mitigation_state spectre_v2_get_cpu_fw_mitigation_state(void) { int ret; diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c index 9824025ccc5c..25ea4ecb6449 100644 --- a/arch/arm64/kvm/hypercalls.c +++ b/arch/arm64/kvm/hypercalls.c @@ -31,7 +31,7 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu) val = SMCCC_RET_SUCCESS; break; case SPECTRE_UNAFFECTED: - val = SMCCC_RET_NOT_REQUIRED; + val = SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED; break; } break; diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h index 15c706fb0a37..0e50ba3e88d7 100644 --- a/include/linux/arm-smccc.h +++ b/include/linux/arm-smccc.h @@ -86,6 +86,8 @@ ARM_SMCCC_SMC_32, \ 0, 0x7fff) +#define SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED 1 + /* Paravirtualised time calls (defined by ARM DEN0057A) */ #define ARM_SMCCC_HV_PV_TIME_FEATURES \ ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL, \ base-commit: 66dd3474702aa98d5844367e1577cdad78ef7c65 -- Sent by a computer, using git, on the internet
