arm/arm64: KVM: make the value of ICC_SRE_EL1 a per-VM variable

ICC_SRE_EL1 is a system register allowing msr/mrs accesses to the
GIC CPU interface for EL1 (guests). Currently we force it to 0, but
for proper GICv3 support we have to allow guests to use it (depending
on their selected virtual GIC model).
So add ICC_SRE_EL1 to the list of saved/restored registers on a
world switch, but actually disallow a guest to change it by only
restoring a fixed, once-initialized value.
This value depends on the GIC model userland has chosen for a guest.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

4 files changed, 17 insertions, 7 deletions

diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index 9a9fce090d58..9d34486985fd 100644
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -140,6 +140,7 @@ int main(void)
   DEFINE(VGIC_V2_CPU_ELRSR,     offsetof(struct vgic_cpu, vgic_v2.vgic_elrsr));
   DEFINE(VGIC_V2_CPU_APR,       offsetof(struct vgic_cpu, vgic_v2.vgic_apr));
   DEFINE(VGIC_V2_CPU_LR,        offsetof(struct vgic_cpu, vgic_v2.vgic_lr));
+  DEFINE(VGIC_V3_CPU_SRE,       offsetof(struct vgic_cpu, vgic_v3.vgic_sre));
   DEFINE(VGIC_V3_CPU_HCR,       offsetof(struct vgic_cpu, vgic_v3.vgic_hcr));
   DEFINE(VGIC_V3_CPU_VMCR,      offsetof(struct vgic_cpu, vgic_v3.vgic_vmcr));
   DEFINE(VGIC_V3_CPU_MISR,      offsetof(struct vgic_cpu, vgic_v3.vgic_misr));
diff --git a/arch/arm64/kvm/vgic-v3-switch.S b/arch/arm64/kvm/vgic-v3-switch.S
index d16046999e06..617a012a0107 100644
--- a/arch/arm64/kvm/vgic-v3-switch.S
+++ b/arch/arm64/kvm/vgic-v3-switch.S
@@ -148,17 +148,18 @@
  * x0: Register pointing to VCPU struct
  */
 .macro  restore_vgic_v3_state
-        // Disable SRE_EL1 access. Necessary, otherwise
-        // ICH_VMCR_EL2.VFIQEn becomes one, and FIQ happens...
-        msr_s   ICC_SRE_EL1, xzr
-        isb
-
         // Compute the address of struct vgic_cpu
         add     x3, x0, #VCPU_VGIC_CPU
 
         // Restore all interesting registers
         ldr     w4, [x3, #VGIC_V3_CPU_HCR]
         ldr     w5, [x3, #VGIC_V3_CPU_VMCR]
+        ldr     w25, [x3, #VGIC_V3_CPU_SRE]
+
+        msr_s   ICC_SRE_EL1, x25
+
+        // make sure SRE is valid before writing the other registers
+        isb
 
         msr_s   ICH_HCR_EL2, x4
         msr_s   ICH_VMCR_EL2, x5
@@ -244,9 +245,12 @@
         dsb     sy
 
         // Prevent the guest from touching the GIC system registers
+        // if SRE isn't enabled for GICv3 emulation
+        cbnz    x25, 1f
         mrs_s   x5, ICC_SRE_EL2
         and     x5, x5, #~ICC_SRE_EL2_ENABLE
         msr_s   ICC_SRE_EL2, x5
+1:
 .endm
 
 ENTRY(__save_vgic_v3_state)
diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
index 1c0e9dbabe6d..ff04afd0d901 100644
--- a/include/kvm/arm_vgic.h
+++ b/include/kvm/arm_vgic.h
@@ -245,6 +245,7 @@ struct vgic_v3_cpu_if {
 #ifdef CONFIG_ARM_GIC_V3
         u32             vgic_hcr;
         u32             vgic_vmcr;
+        u32             vgic_sre;       /* Restored only, change ignored */
         u32             vgic_misr;      /* Saved only */
         u32             vgic_eisr;      /* Saved only */
         u32             vgic_elrsr;     /* Saved only */
diff --git a/virt/kvm/arm/vgic-v3.c b/virt/kvm/arm/vgic-v3.c
index ea39bad4b004..52490480b6f9 100644
--- a/virt/kvm/arm/vgic-v3.c
+++ b/virt/kvm/arm/vgic-v3.c
@@ -145,15 +145,19 @@ static void vgic_v3_set_vmcr(struct kvm_vcpu *vcpu, struct vgic_vmcr *vmcrp)
 
 static void vgic_v3_enable(struct kvm_vcpu *vcpu)
 {
+        struct vgic_v3_cpu_if *vgic_v3 = &vcpu->arch.vgic_cpu.vgic_v3;
+
         /*
          * By forcing VMCR to zero, the GIC will restore the binary
          * points to their reset values. Anything else resets to zero
          * anyway.
          */
-        vcpu->arch.vgic_cpu.vgic_v3.vgic_vmcr = 0;
+        vgic_v3->vgic_vmcr = 0;
+
+        vgic_v3->vgic_sre = 0;
 
         /* Get the show on the road... */
-        vcpu->arch.vgic_cpu.vgic_v3.vgic_hcr = ICH_HCR_EN;
+        vgic_v3->vgic_hcr = ICH_HCR_EN;
 }
 
 static const struct vgic_ops vgic_v3_ops = {