KVM: arm64: Don't set HCR_EL2.TVM when S2FWB is supported
On CPUs that support S2FWB (Armv8.4+), KVM configures the stage 2 page
tables to override the memory attributes of memory accesses, regardless
of the stage 1 page table configurations, and also when the stage 1 MMU
is turned off. This results in all memory accesses to RAM being
cacheable, including during early boot of the guest.
On CPUs without this feature, memory accesses were non-cacheable during
boot until the guest turned on the stage 1 MMU, and we had to detect
when the guest turned on the MMU, such that we could invalidate all cache
entries and ensure a consistent view of memory with the MMU turned on.
When the guest turned on the caches, we would call stage2_flush_vm()
from kvm_toggle_cache().
However, stage2_flush_vm() walks all the stage 2 tables, and calls
__kvm_flush-dcache_pte, which on a system with S2FWB does ... absolutely
nothing.
We can avoid that whole song and dance, and simply not set TVM when
creating a VM on a system that has S2FWB.
Signed-off-by: Christoffer Dall <christoffer.dall@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20191028130541.30536-1-christoffer.dall@arm.com
diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index d69c1ef..6e92f6c 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -53,8 +53,18 @@ static inline void vcpu_reset_hcr(struct kvm_vcpu *vcpu)
/* trap error record accesses */
vcpu->arch.hcr_el2 |= HCR_TERR;
}
- if (cpus_have_const_cap(ARM64_HAS_STAGE2_FWB))
+
+ if (cpus_have_const_cap(ARM64_HAS_STAGE2_FWB)) {
vcpu->arch.hcr_el2 |= HCR_FWB;
+ } else {
+ /*
+ * For non-FWB CPUs, we trap VM ops (HCR_EL2.TVM) until M+C
+ * get set in SCTLR_EL1 such that we can detect when the guest
+ * MMU gets turned on and do the necessary cache maintenance
+ * then.
+ */
+ vcpu->arch.hcr_el2 |= HCR_TVM;
+ }
if (test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features))
vcpu->arch.hcr_el2 &= ~HCR_RW;