[PATCH 54/89] KVM: arm64: Reduce host/shadow vcpu state copying

[Will Deacon]

From: Marc Zyngier <maz at kernel.org>

When running with pKVM enabled, protected guests run with a fixed CPU
configuration and therefore features such as hardware debug and SVE are
unavailable and their state does not need to be copied from the host
structures on each flush operation. Although non-protected guests do
require the host and shadow structures to be kept in-sync with each
other, we can defer writing back to the host to an explicit sync
hypercall, rather than doing it after every vCPU run.

Signed-off-by: Marc Zyngier <maz at kernel.org>
---
 arch/arm64/kvm/hyp/nvhe/hyp-main.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index 228736a9ab40..e82c0faf6c81 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -196,17 +196,18 @@ static void flush_shadow_state(struct kvm_shadow_vcpu_state *shadow_state)
 
 		if (host_flags & KVM_ARM64_PKVM_STATE_DIRTY)
 			__flush_vcpu_state(shadow_state);
-	}
 
-	shadow_vcpu->arch.sve_state	= kern_hyp_va(host_vcpu->arch.sve_state);
-	shadow_vcpu->arch.sve_max_vl	= host_vcpu->arch.sve_max_vl;
+		shadow_vcpu->arch.sve_state = kern_hyp_va(host_vcpu->arch.sve_state);
+		shadow_vcpu->arch.sve_max_vl = host_vcpu->arch.sve_max_vl;
 
-	shadow_vcpu->arch.hcr_el2	= host_vcpu->arch.hcr_el2;
-	shadow_vcpu->arch.mdcr_el2	= host_vcpu->arch.mdcr_el2;
+		shadow_vcpu->arch.hcr_el2 = HCR_GUEST_FLAGS & ~(HCR_RW | HCR_TWI | HCR_TWE);
+		shadow_vcpu->arch.hcr_el2 |= READ_ONCE(host_vcpu->arch.hcr_el2);
 
-	shadow_vcpu->arch.debug_ptr	= kern_hyp_va(host_vcpu->arch.debug_ptr);
+		shadow_vcpu->arch.mdcr_el2 = host_vcpu->arch.mdcr_el2;
+		shadow_vcpu->arch.debug_ptr = kern_hyp_va(host_vcpu->arch.debug_ptr);
+	}
 
-	shadow_vcpu->arch.vsesr_el2	= host_vcpu->arch.vsesr_el2;
+	shadow_vcpu->arch.vsesr_el2 = host_vcpu->arch.vsesr_el2;
 
 	flush_vgic_state(host_vcpu, shadow_vcpu);
 	flush_timer_state(shadow_state);
@@ -238,10 +239,10 @@ static void sync_shadow_state(struct kvm_shadow_vcpu_state *shadow_state,
 	unsigned long host_flags;
 	u8 esr_ec;
 
-	host_vcpu->arch.ctxt		= shadow_vcpu->arch.ctxt;
-
-	host_vcpu->arch.hcr_el2		= shadow_vcpu->arch.hcr_el2;
-
+	/*
+	 * Don't sync the vcpu GPR/sysreg state after a run. Instead,
+	 * leave it in the shadow until someone actually requires it.
+	 */
 	sync_vgic_state(host_vcpu, shadow_vcpu);
 	sync_timer_state(shadow_state);
 
-- 
2.36.1.124.g0e6072fb45-goog