KVM: arm64: vgic-v4: Make the doorbell request robust w.r.t preemption

Xiang reports that VMs occasionally fail to boot on GICv4.1 systems when
running a preemptible kernel, as it is possible that a vCPU is blocked
without requesting a doorbell interrupt.

The issue is that any preemption that occurs between vgic_v4_put() and
schedule() on the block path will mark the vPE as nonresident and *not*
request a doorbell irq. This occurs because when the vcpu thread is
resumed on its way to block, vcpu_load() will make the vPE resident
again. Once the vcpu actually blocks, we don't request a doorbell
anymore, and the vcpu won't be woken up on interrupt delivery.

Fix it by tracking that we're entering WFI, and key the doorbell
request on that flag. This allows us not to make the vPE resident
when going through a preempt/schedule cycle, meaning we don't lose
any state.

Cc: stable@vger.kernel.org
Fixes: 8e01d9a396e6 ("KVM: arm64: vgic-v4: Move the GICv4 residency flow to be driven by vcpu_load/put")
Reported-by: Xiang Chen <chenxiang66@hisilicon.com>
Suggested-by: Zenghui Yu <yuzenghui@huawei.com>
Tested-by: Xiang Chen <chenxiang66@hisilicon.com>
Co-developed-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Acked-by: Zenghui Yu <yuzenghui@huawei.com>
Link: https://lore.kernel.org/r/20230713070657.3873244-1-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 8b60967..d3dd05b 100644 (file)
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -727,6 +727,8 @@ struct kvm_vcpu_arch {
 #define DBG_SS_ACTIVE_PENDING  __vcpu_single_flag(sflags, BIT(5))
 /* PMUSERENR for the guest EL0 is on physical CPU */
 #define PMUSERENR_ON_CPU       __vcpu_single_flag(sflags, BIT(6))
+/* WFI instruction trapped */
+#define IN_WFI                 __vcpu_single_flag(sflags, BIT(7))
 
 
 /* Pointer to the vcpu's SVE FFR for sve_{save,load}_state() */

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index a402ea5..72dc53a 100644 (file)
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -718,13 +718,15 @@ void kvm_vcpu_wfi(struct kvm_vcpu *vcpu)
         */
        preempt_disable();
        kvm_vgic_vmcr_sync(vcpu);
-       vgic_v4_put(vcpu, true);
+       vcpu_set_flag(vcpu, IN_WFI);
+       vgic_v4_put(vcpu);
        preempt_enable();
 
        kvm_vcpu_halt(vcpu);
        vcpu_clear_flag(vcpu, IN_WFIT);
 
        preempt_disable();
+       vcpu_clear_flag(vcpu, IN_WFI);
        vgic_v4_load(vcpu);
        preempt_enable();
 }
@@ -792,7 +794,7 @@ static int check_vcpu_requests(struct kvm_vcpu *vcpu)
                if (kvm_check_request(KVM_REQ_RELOAD_GICv4, vcpu)) {
                        /* The distributor enable bits were changed */
                        preempt_disable();
-                       vgic_v4_put(vcpu, false);
+                       vgic_v4_put(vcpu);
                        vgic_v4_load(vcpu);
                        preempt_enable();
                }

diff --git a/arch/arm64/kvm/vgic/vgic-v3.c b/arch/arm64/kvm/vgic/vgic-v3.c
index c3b8e13..3dfc8b8 100644 (file)
--- a/arch/arm64/kvm/vgic/vgic-v3.c
+++ b/arch/arm64/kvm/vgic/vgic-v3.c
@@ -749,7 +749,7 @@ void vgic_v3_put(struct kvm_vcpu *vcpu)
 {
        struct vgic_v3_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v3;
 
-       WARN_ON(vgic_v4_put(vcpu, false));
+       WARN_ON(vgic_v4_put(vcpu));
 
        vgic_v3_vmcr_sync(vcpu);
 

diff --git a/arch/arm64/kvm/vgic/vgic-v4.c b/arch/arm64/kvm/vgic/vgic-v4.c
index c1c28fe..339a551 100644 (file)
--- a/arch/arm64/kvm/vgic/vgic-v4.c
+++ b/arch/arm64/kvm/vgic/vgic-v4.c
@@ -336,14 +336,14 @@ void vgic_v4_teardown(struct kvm *kvm)
        its_vm->vpes = NULL;
 }
 
-int vgic_v4_put(struct kvm_vcpu *vcpu, bool need_db)
+int vgic_v4_put(struct kvm_vcpu *vcpu)
 {
        struct its_vpe *vpe = &vcpu->arch.vgic_cpu.vgic_v3.its_vpe;
 
        if (!vgic_supports_direct_msis(vcpu->kvm) || !vpe->resident)
                return 0;
 
-       return its_make_vpe_non_resident(vpe, need_db);
+       return its_make_vpe_non_resident(vpe, !!vcpu_get_flag(vcpu, IN_WFI));
 }
 
 int vgic_v4_load(struct kvm_vcpu *vcpu)
@@ -354,6 +354,9 @@ int vgic_v4_load(struct kvm_vcpu *vcpu)
        if (!vgic_supports_direct_msis(vcpu->kvm) || vpe->resident)
                return 0;
 
+       if (vcpu_get_flag(vcpu, IN_WFI))
+               return 0;
+
        /*
         * Before making the VPE resident, make sure the redistributor
         * corresponding to our current CPU expects us here. See the

diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
index 402b545..5b27f94 100644 (file)
--- a/include/kvm/arm_vgic.h
+++ b/include/kvm/arm_vgic.h
@@ -431,7 +431,7 @@ int kvm_vgic_v4_unset_forwarding(struct kvm *kvm, int irq,
 
 int vgic_v4_load(struct kvm_vcpu *vcpu);
 void vgic_v4_commit(struct kvm_vcpu *vcpu);
-int vgic_v4_put(struct kvm_vcpu *vcpu, bool need_db);
+int vgic_v4_put(struct kvm_vcpu *vcpu);
 
 /* CPU HP callbacks */
 void kvm_vgic_cpu_up(void);