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

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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: 8e01d9a396 ("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>
This commit is contained in:
Marc Zyngier 2023-07-13 08:06:57 +01:00 committed by Oliver Upton
parent dcf89d1111
commit b321c31c9b
5 changed files with 13 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/arm64/include/asm/kvm_host.h
View File

@ -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() */

6
arch/arm64/kvm/arm.c
View File

@ -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();
}

2
arch/arm64/kvm/vgic/vgic-v3.c
View File

@ -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);

7
arch/arm64/kvm/vgic/vgic-v4.c
View File

@ -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

2
include/kvm/arm_vgic.h
View File

@ -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);