[PATCH v1 4/4] KVM: arm64: Initialize trap register values in hyp in pKVM

[Fuad Tabba <tabba@google.com>]

Handle the initialization of trap registers at the hypervisor in
pKVM, even for non-protected guests. The host is not trusted with
the values of the trap registers, regardless of the VM type.
Therefore, when switching between the host and the guests, only
flush the required bits of the trap registers from the host's
view that are required for hyp-host communication.

Reported-by: Will Deacon <will@kernel.org>
Fixes: 814ad8f96e92 ("KVM: arm64: Drop trapping of PAuth instructions/keys")
Signed-off-by: Fuad Tabba <tabba@google.com>
---
 arch/arm64/kvm/hyp/nvhe/hyp-main.c |  4 +++-
 arch/arm64/kvm/hyp/nvhe/pkvm.c     | 35 ++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index 1a224d5df207..6aa0b13d86e5 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -105,8 +105,10 @@ static void flush_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu)
 
 	hyp_vcpu->vcpu.arch.hw_mmu	= host_vcpu->arch.hw_mmu;
 
-	hyp_vcpu->vcpu.arch.hcr_el2	= host_vcpu->arch.hcr_el2;
 	hyp_vcpu->vcpu.arch.mdcr_el2	= host_vcpu->arch.mdcr_el2;
+	hyp_vcpu->vcpu.arch.hcr_el2 &= ~(HCR_TWI | HCR_TWE);
+	hyp_vcpu->vcpu.arch.hcr_el2 |= READ_ONCE(host_vcpu->arch.hcr_el2) &
+						 (HCR_TWI | HCR_TWE);
 
 	hyp_vcpu->vcpu.arch.iflags	= host_vcpu->arch.iflags;
 
diff --git a/arch/arm64/kvm/hyp/nvhe/pkvm.c b/arch/arm64/kvm/hyp/nvhe/pkvm.c
index 954df57a935f..01616c39a810 100644
--- a/arch/arm64/kvm/hyp/nvhe/pkvm.c
+++ b/arch/arm64/kvm/hyp/nvhe/pkvm.c
@@ -204,11 +204,46 @@ static void pvm_init_trap_regs(struct kvm_vcpu *vcpu)
 	}
 }
 
+static void pkvm_vcpu_reset_hcr(struct kvm_vcpu *vcpu)
+{
+	vcpu->arch.hcr_el2 = HCR_GUEST_FLAGS;
+
+	if (has_hvhe())
+		vcpu->arch.hcr_el2 |= HCR_E2H;
+
+	if (cpus_have_final_cap(ARM64_HAS_RAS_EXTN)) {
+		/* route synchronous external abort exceptions to EL2 */
+		vcpu->arch.hcr_el2 |= HCR_TEA;
+		/* trap error record accesses */
+		vcpu->arch.hcr_el2 |= HCR_TERR;
+	}
+
+	if (cpus_have_final_cap(ARM64_HAS_STAGE2_FWB))
+		vcpu->arch.hcr_el2 |= HCR_FWB;
+
+	if (cpus_have_final_cap(ARM64_HAS_EVT) &&
+	    !cpus_have_final_cap(ARM64_MISMATCHED_CACHE_TYPE))
+		vcpu->arch.hcr_el2 |= HCR_TID4;
+	else
+		vcpu->arch.hcr_el2 |= HCR_TID2;
+
+	if (vcpu_has_ptrauth(vcpu))
+		vcpu->arch.hcr_el2 |= (HCR_API | HCR_APK);
+}
+
 /*
  * Initialize trap register values in protected mode.
  */
 static void pkvm_vcpu_init_traps(struct kvm_vcpu *vcpu)
 {
+	vcpu->arch.cptr_el2 = kvm_get_reset_cptr_el2(vcpu);
+	vcpu->arch.mdcr_el2 = 0;
+
+	pkvm_vcpu_reset_hcr(vcpu);
+
+	if ((!vcpu_is_protected(vcpu)))
+		return;
+
 	pvm_init_trap_regs(vcpu);
 	pvm_init_traps_aa64pfr0(vcpu);
 	pvm_init_traps_aa64pfr1(vcpu);
-- 
2.47.0.rc1.288.g06298d1525-goog