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: Moving SMCCC_RET_NOT_AFFECTED to a header is left out of this patch as it would need to move from proton-pack.c which isn't in stable trees and the name isn't actually part of the SMCCC spec)

Cc: Andre Przywara andre.przywara@arm.com Cc: Steven Price steven.price@arm.com Cc: Marc Zyngier maz@kernel.org Cc: stable@vger.kernel.org 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@chromium.org ---

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 v1: * Way longer commit text, more background (sorry) * Dropped proton-pack part because it was wrong * Rebased onto other patch accepted upstream

arch/arm64/kvm/hypercalls.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c index 9824025ccc5c..6a62312d7813 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 = 1; break; } break;

base-commit: 66dd3474702aa98d5844367e1577cdad78ef7c65