On Fri, Oct 23, 2020 at 08:47:50AM -0700, Stephen Boyd wrote: > 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 I thought we'd stick this in asm/spectre.h, but here is also good: Acked-by: Will Deacon <will@xxxxxxxxxx> Will
