On SMP ARM systems, cache maintenance by set/way should only ever be done in the context of onlining or offlining CPUs, which is typically done by bare metal firmware and never in a virtual machine. For this reason, we trap set/way cache maintenance operations and replace them with conditional flushing of the entire guest address space. Due to this trapping, the set/way arguments passed into the set/way ops are completely ignored, and thus irrelevant. This also means that the set/way geometry is equally irrelevant, and we can simply report it as 1 set and 1 way, so that legacy 32-bit ARM system software (i.e., the kind that only receives odd fixes) doesn't take a performance hit due to the trapping when iterating over the cachelines. Acked-by: Christoffer Dall <christoffer.dall@xxxxxxx> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> --- arch/arm64/include/asm/kvm_emulate.h | 3 ++- arch/arm64/kvm/sys_regs.c | 15 +++++++++++++++ 2 files changed, 17 insertions(+), 1 deletion(-) diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h index 87f9c1b6387e..c450b15511b7 100644 --- a/arch/arm64/include/asm/kvm_emulate.h +++ b/arch/arm64/include/asm/kvm_emulate.h @@ -78,7 +78,8 @@ static inline void vcpu_reset_hcr(struct kvm_vcpu *vcpu) if (!vcpu_el1_is_32bit(vcpu)) vcpu->arch.hcr_el2 |= HCR_TID3; - if (cpus_have_const_cap(ARM64_MISMATCHED_CACHE_TYPE)) + if (cpus_have_const_cap(ARM64_MISMATCHED_CACHE_TYPE) || + vcpu_el1_is_32bit(vcpu)) vcpu->arch.hcr_el2 |= HCR_TID2; } diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c index 1312aebf74e6..5882e3410acc 100644 --- a/arch/arm64/kvm/sys_regs.c +++ b/arch/arm64/kvm/sys_regs.c @@ -1188,6 +1188,21 @@ static bool access_ccsidr(struct kvm_vcpu *vcpu, struct sys_reg_params *p, csselr = vcpu_read_sys_reg(vcpu, CSSELR_EL1); p->regval = get_ccsidr(csselr); + + /* + * Guests should not be doing cache operations by set/way at all, and + * for this reason, we trap them and attempt to infer the intent, so + * that we can flush the entire guest's address space at the appropriate + * time. + * To prevent this trapping from causing performance problems, let's + * expose the geometry of all data and unified caches (which are + * guaranteed to be PIPT and thus non-aliasing) as 1 set and 1 way. + * [If guests should attempt to infer aliasing properties from the + * geometry (which is not permitted by the architecture), they would + * only do so for virtually indexed caches.] + */ + if (!(csselr & 1)) // data or unified cache + p->regval &= ~GENMASK(27, 3); return true; } -- 2.20.1 _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
