[patch 0/3] VMX: configure posted interrupt descriptor when assigning device (v5)

[patch 0/3] VMX: configure posted interrupt descriptor when assigning device (v5)

[Marcelo Tosatti]

Configuration of the posted interrupt descriptor is incorrect when devices
are hotplugged to the guest (and vcpus are halted).

See patch 3 for details.

---

v5: use KVM_REQ_UNBLOCK instead of kvm_check_block callback (Paolo / Peter Xu)

v4: remove NULL assignments from kvm_x86_ops (Peter Xu)
    check for return value of ->start_assignment directly (Peter Xu)

v3: improved comments (Sean)
    use kvm_vcpu_wake_up (Sean)
    drop device_count from start_assignment function (Peter Xu)

v2: rather than using a potentially racy IPI (vs vcpu->cpu switches),
    kick the vcpus when assigning a device and let the blocked per-CPU
    list manipulation happen locally at ->pre_block and ->post_block
    (Sean Christopherson).

[patch 1/3] KVM: x86: add start_assignment hook to kvm_x86_ops

[Marcelo Tosatti]

Add a start_assignment hook to kvm_x86_ops, which is called when 
kvm_arch_start_assignment is done.

The hook is required to update the wakeup vector of a sleeping vCPU
when a device is assigned to the guest.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

Index: kvm/arch/x86/include/asm/kvm_host.h
===================================================================
--- kvm.orig/arch/x86/include/asm/kvm_host.h
+++ kvm/arch/x86/include/asm/kvm_host.h
@@ -1322,6 +1322,7 @@ struct kvm_x86_ops {
 
 	int (*update_pi_irte)(struct kvm *kvm, unsigned int host_irq,
 			      uint32_t guest_irq, bool set);
+	void (*start_assignment)(struct kvm *kvm);
 	void (*apicv_post_state_restore)(struct kvm_vcpu *vcpu);
 	bool (*dy_apicv_has_pending_interrupt)(struct kvm_vcpu *vcpu);
 
Index: kvm/arch/x86/kvm/x86.c
===================================================================
--- kvm.orig/arch/x86/kvm/x86.c
+++ kvm/arch/x86/kvm/x86.c
@@ -11295,7 +11295,8 @@ bool kvm_arch_can_dequeue_async_page_pre
 
 void kvm_arch_start_assignment(struct kvm *kvm)
 {
-	atomic_inc(&kvm->arch.assigned_device_count);
+	if (atomic_inc_return(&kvm->arch.assigned_device_count) == 1)
+		static_call_cond(kvm_x86_start_assignment)(kvm);
 }
 EXPORT_SYMBOL_GPL(kvm_arch_start_assignment);
 
Index: kvm/arch/x86/include/asm/kvm-x86-ops.h
===================================================================
--- kvm.orig/arch/x86/include/asm/kvm-x86-ops.h
+++ kvm/arch/x86/include/asm/kvm-x86-ops.h
@@ -99,6 +99,7 @@ KVM_X86_OP_NULL(post_block)
 KVM_X86_OP_NULL(vcpu_blocking)
 KVM_X86_OP_NULL(vcpu_unblocking)
 KVM_X86_OP_NULL(update_pi_irte)
+KVM_X86_OP_NULL(start_assignment)
 KVM_X86_OP_NULL(apicv_post_state_restore)
 KVM_X86_OP_NULL(dy_apicv_has_pending_interrupt)
 KVM_X86_OP_NULL(set_hv_timer)

[patch 2/3] KVM: rename KVM_REQ_PENDING_TIMER to KVM_REQ_UNBLOCK

[Marcelo Tosatti]

KVM_REQ_UNBLOCK will be used to exit a vcpu from
its inner vcpu halt emulation loop.

Rename KVM_REQ_PENDING_TIMER to KVM_REQ_UNBLOCK, switch
PowerPC to arch specific request bit.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

Index: kvm/include/linux/kvm_host.h
===================================================================
--- kvm.orig/include/linux/kvm_host.h
+++ kvm/include/linux/kvm_host.h
@@ -146,7 +146,7 @@ static inline bool is_error_page(struct
  */
 #define KVM_REQ_TLB_FLUSH         (0 | KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
 #define KVM_REQ_MMU_RELOAD        (1 | KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
-#define KVM_REQ_PENDING_TIMER     2
+#define KVM_REQ_UNBLOCK           2
 #define KVM_REQ_UNHALT            3
 #define KVM_REQUEST_ARCH_BASE     8
 
Index: kvm/virt/kvm/kvm_main.c
===================================================================
--- kvm.orig/virt/kvm/kvm_main.c
+++ kvm/virt/kvm/kvm_main.c
@@ -2794,6 +2794,8 @@ static int kvm_vcpu_check_block(struct k
 		goto out;
 	if (signal_pending(current))
 		goto out;
+	if (kvm_check_request(KVM_REQ_UNBLOCK, vcpu))
+		goto out;
 
 	ret = 0;
 out:
Index: kvm/Documentation/virt/kvm/vcpu-requests.rst
===================================================================
--- kvm.orig/Documentation/virt/kvm/vcpu-requests.rst
+++ kvm/Documentation/virt/kvm/vcpu-requests.rst
@@ -118,10 +118,11 @@ KVM_REQ_MMU_RELOAD
   necessary to inform each VCPU to completely refresh the tables.  This
   request is used for that.
 
-KVM_REQ_PENDING_TIMER
+KVM_REQ_UNBLOCK
 
   This request may be made from a timer handler run on the host on behalf
-  of a VCPU.  It informs the VCPU thread to inject a timer interrupt.
+  of a VCPU, or when device assignment is performed. It informs the VCPU to
+  exit the vcpu halt inner loop.
 
 KVM_REQ_UNHALT
 
Index: kvm/arch/powerpc/include/asm/kvm_host.h
===================================================================
--- kvm.orig/arch/powerpc/include/asm/kvm_host.h
+++ kvm/arch/powerpc/include/asm/kvm_host.h
@@ -51,6 +51,7 @@
 /* PPC-specific vcpu->requests bit members */
 #define KVM_REQ_WATCHDOG	KVM_ARCH_REQ(0)
 #define KVM_REQ_EPR_EXIT	KVM_ARCH_REQ(1)
+#define KVM_REQ_PENDING_TIMER	KVM_ARCH_REQ(2)
 
 #include <linux/mmu_notifier.h>
 
Index: kvm/arch/x86/kvm/lapic.c
===================================================================
--- kvm.orig/arch/x86/kvm/lapic.c
+++ kvm/arch/x86/kvm/lapic.c
@@ -1657,7 +1657,7 @@ static void apic_timer_expired(struct kv
 	}
 
 	atomic_inc(&apic->lapic_timer.pending);
-	kvm_make_request(KVM_REQ_PENDING_TIMER, vcpu);
+	kvm_make_request(KVM_REQ_UNBLOCK, vcpu);
 	if (from_timer_fn)
 		kvm_vcpu_kick(vcpu);
 }
Index: kvm/arch/x86/kvm/x86.c
===================================================================
--- kvm.orig/arch/x86/kvm/x86.c
+++ kvm/arch/x86/kvm/x86.c
@@ -9300,7 +9300,7 @@ static int vcpu_run(struct kvm_vcpu *vcp
 		if (r <= 0)
 			break;
 
-		kvm_clear_request(KVM_REQ_PENDING_TIMER, vcpu);
+		kvm_clear_request(KVM_REQ_UNBLOCK, vcpu);
 		if (kvm_cpu_has_pending_timer(vcpu))
 			kvm_inject_pending_timer_irqs(vcpu);
 

[patch 3/3] KVM: VMX: update vcpu posted-interrupt descriptor when assigning device

[Marcelo Tosatti]

For VMX, when a vcpu enters HLT emulation, pi_post_block will:

1) Add vcpu to per-cpu list of blocked vcpus.

2) Program the posted-interrupt descriptor "notification vector" 
to POSTED_INTR_WAKEUP_VECTOR

With interrupt remapping, an interrupt will set the PIR bit for the 
vector programmed for the device on the CPU, test-and-set the 
ON bit on the posted interrupt descriptor, and if the ON bit is clear
generate an interrupt for the notification vector.

This way, the target CPU wakes upon a device interrupt and wakes up
the target vcpu.

Problem is that pi_post_block only programs the notification vector
if kvm_arch_has_assigned_device() is true. Its possible for the
following to happen:

1) vcpu V HLTs on pcpu P, kvm_arch_has_assigned_device is false,
notification vector is not programmed
2) device is assigned to VM
3) device interrupts vcpu V, sets ON bit
(notification vector not programmed, so pcpu P remains in idle)
4) vcpu 0 IPIs vcpu V (in guest), but since pi descriptor ON bit is set,
kvm_vcpu_kick is skipped
5) vcpu 0 busy spins on vcpu V's response for several seconds, until
RCU watchdog NMIs all vCPUs.

To fix this, use the start_assignment kvm_x86_ops callback to kick
vcpus out of the halt loop, so the notification vector is 
properly reprogrammed to the wakeup vector.

Reported-by: Pei Zhang <pezhang@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>


Index: kvm/arch/x86/kvm/vmx/posted_intr.c
===================================================================
--- kvm.orig/arch/x86/kvm/vmx/posted_intr.c
+++ kvm/arch/x86/kvm/vmx/posted_intr.c
@@ -236,6 +236,13 @@ bool pi_has_pending_interrupt(struct kvm
 		(pi_test_sn(pi_desc) && !pi_is_pir_empty(pi_desc));
 }
 
+void vmx_pi_start_assignment(struct kvm *kvm)
+{
+	if (!irq_remapping_cap(IRQ_POSTING_CAP))
+		return;
+
+	kvm_make_all_cpus_request(kvm, KVM_REQ_UNBLOCK);
+}
 
 /*
  * pi_update_irte - set IRTE for Posted-Interrupts
Index: kvm/arch/x86/kvm/vmx/posted_intr.h
===================================================================
--- kvm.orig/arch/x86/kvm/vmx/posted_intr.h
+++ kvm/arch/x86/kvm/vmx/posted_intr.h
@@ -95,5 +95,6 @@ void __init pi_init_cpu(int cpu);
 bool pi_has_pending_interrupt(struct kvm_vcpu *vcpu);
 int pi_update_irte(struct kvm *kvm, unsigned int host_irq, uint32_t guest_irq,
 		   bool set);
+void vmx_pi_start_assignment(struct kvm *kvm);
 
 #endif /* __KVM_X86_VMX_POSTED_INTR_H */
Index: kvm/arch/x86/kvm/vmx/vmx.c
===================================================================
--- kvm.orig/arch/x86/kvm/vmx/vmx.c
+++ kvm/arch/x86/kvm/vmx/vmx.c
@@ -7732,6 +7732,7 @@ static struct kvm_x86_ops vmx_x86_ops __
 	.nested_ops = &vmx_nested_ops,
 
 	.update_pi_irte = pi_update_irte,
+	.start_assignment = vmx_pi_start_assignment,
 
 #ifdef CONFIG_X86_64
 	.set_hv_timer = vmx_set_hv_timer,

Re: [patch 2/3] KVM: rename KVM_REQ_PENDING_TIMER to KVM_REQ_UNBLOCK

[Peter Xu]

On Tue, May 25, 2021 at 10:41:17AM -0300, Marcelo Tosatti wrote:
> KVM_REQ_UNBLOCK will be used to exit a vcpu from
> its inner vcpu halt emulation loop.
> 
> Rename KVM_REQ_PENDING_TIMER to KVM_REQ_UNBLOCK, switch
> PowerPC to arch specific request bit.
> 
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
> 
> Index: kvm/include/linux/kvm_host.h
> ===================================================================
> --- kvm.orig/include/linux/kvm_host.h
> +++ kvm/include/linux/kvm_host.h
> @@ -146,7 +146,7 @@ static inline bool is_error_page(struct
>   */
>  #define KVM_REQ_TLB_FLUSH         (0 | KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
>  #define KVM_REQ_MMU_RELOAD        (1 | KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
> -#define KVM_REQ_PENDING_TIMER     2
> +#define KVM_REQ_UNBLOCK           2
>  #define KVM_REQ_UNHALT            3
>  #define KVM_REQUEST_ARCH_BASE     8
>  
> Index: kvm/virt/kvm/kvm_main.c
> ===================================================================
> --- kvm.orig/virt/kvm/kvm_main.c
> +++ kvm/virt/kvm/kvm_main.c
> @@ -2794,6 +2794,8 @@ static int kvm_vcpu_check_block(struct k
>  		goto out;
>  	if (signal_pending(current))
>  		goto out;
> +	if (kvm_check_request(KVM_REQ_UNBLOCK, vcpu))
> +		goto out;
>  
>  	ret = 0;
>  out:
> Index: kvm/Documentation/virt/kvm/vcpu-requests.rst
> ===================================================================
> --- kvm.orig/Documentation/virt/kvm/vcpu-requests.rst
> +++ kvm/Documentation/virt/kvm/vcpu-requests.rst
> @@ -118,10 +118,11 @@ KVM_REQ_MMU_RELOAD
>    necessary to inform each VCPU to completely refresh the tables.  This
>    request is used for that.
>  
> -KVM_REQ_PENDING_TIMER
> +KVM_REQ_UNBLOCK
>  
>    This request may be made from a timer handler run on the host on behalf
> -  of a VCPU.  It informs the VCPU thread to inject a timer interrupt.
> +  of a VCPU, or when device assignment is performed. It informs the VCPU to
> +  exit the vcpu halt inner loop.
>  
>  KVM_REQ_UNHALT
>  
> Index: kvm/arch/powerpc/include/asm/kvm_host.h
> ===================================================================
> --- kvm.orig/arch/powerpc/include/asm/kvm_host.h
> +++ kvm/arch/powerpc/include/asm/kvm_host.h
> @@ -51,6 +51,7 @@
>  /* PPC-specific vcpu->requests bit members */
>  #define KVM_REQ_WATCHDOG	KVM_ARCH_REQ(0)
>  #define KVM_REQ_EPR_EXIT	KVM_ARCH_REQ(1)
> +#define KVM_REQ_PENDING_TIMER	KVM_ARCH_REQ(2)
>  
>  #include <linux/mmu_notifier.h>
>  
> Index: kvm/arch/x86/kvm/lapic.c
> ===================================================================
> --- kvm.orig/arch/x86/kvm/lapic.c
> +++ kvm/arch/x86/kvm/lapic.c
> @@ -1657,7 +1657,7 @@ static void apic_timer_expired(struct kv
>  	}
>  
>  	atomic_inc(&apic->lapic_timer.pending);
> -	kvm_make_request(KVM_REQ_PENDING_TIMER, vcpu);
> +	kvm_make_request(KVM_REQ_UNBLOCK, vcpu);
>  	if (from_timer_fn)
>  		kvm_vcpu_kick(vcpu);
>  }

Pure question on the existing code: why do we need kvm_make_request() for
timer?  As I see kvm_vcpu_check_block() already checks explicitly for timers:

static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu)
{
        ...
	if (kvm_cpu_has_pending_timer(vcpu))
		goto out;
        ...
}

for x86:

int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu)
{
	if (lapic_in_kernel(vcpu))
		return apic_has_pending_timer(vcpu);

	return 0;
}

So wondering why we can drop the two references to KVM_REQ_PENDING_TIMER in x86
directly..

> Index: kvm/arch/x86/kvm/x86.c
> ===================================================================
> --- kvm.orig/arch/x86/kvm/x86.c
> +++ kvm/arch/x86/kvm/x86.c
> @@ -9300,7 +9300,7 @@ static int vcpu_run(struct kvm_vcpu *vcp
>  		if (r <= 0)
>  			break;
>  
> -		kvm_clear_request(KVM_REQ_PENDING_TIMER, vcpu);
> +		kvm_clear_request(KVM_REQ_UNBLOCK, vcpu);
>  		if (kvm_cpu_has_pending_timer(vcpu))
>  			kvm_inject_pending_timer_irqs(vcpu);
>  
> 
> 

-- 
Peter Xu

Re: [patch 2/3] KVM: rename KVM_REQ_PENDING_TIMER to KVM_REQ_UNBLOCK

[Marcelo Tosatti]

On Tue, May 25, 2021 at 03:14:33PM -0400, Peter Xu wrote:
> On Tue, May 25, 2021 at 10:41:17AM -0300, Marcelo Tosatti wrote:
> > KVM_REQ_UNBLOCK will be used to exit a vcpu from
> > its inner vcpu halt emulation loop.
> > 
> > Rename KVM_REQ_PENDING_TIMER to KVM_REQ_UNBLOCK, switch
> > PowerPC to arch specific request bit.
> > 
> > Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
> > 
> > Index: kvm/include/linux/kvm_host.h
> > ===================================================================
> > --- kvm.orig/include/linux/kvm_host.h
> > +++ kvm/include/linux/kvm_host.h
> > @@ -146,7 +146,7 @@ static inline bool is_error_page(struct
> >   */
> >  #define KVM_REQ_TLB_FLUSH         (0 | KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
> >  #define KVM_REQ_MMU_RELOAD        (1 | KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
> > -#define KVM_REQ_PENDING_TIMER     2
> > +#define KVM_REQ_UNBLOCK           2
> >  #define KVM_REQ_UNHALT            3
> >  #define KVM_REQUEST_ARCH_BASE     8
> >  
> > Index: kvm/virt/kvm/kvm_main.c
> > ===================================================================
> > --- kvm.orig/virt/kvm/kvm_main.c
> > +++ kvm/virt/kvm/kvm_main.c
> > @@ -2794,6 +2794,8 @@ static int kvm_vcpu_check_block(struct k
> >  		goto out;
> >  	if (signal_pending(current))
> >  		goto out;
> > +	if (kvm_check_request(KVM_REQ_UNBLOCK, vcpu))
> > +		goto out;
> >  
> >  	ret = 0;
> >  out:
> > Index: kvm/Documentation/virt/kvm/vcpu-requests.rst
> > ===================================================================
> > --- kvm.orig/Documentation/virt/kvm/vcpu-requests.rst
> > +++ kvm/Documentation/virt/kvm/vcpu-requests.rst
> > @@ -118,10 +118,11 @@ KVM_REQ_MMU_RELOAD
> >    necessary to inform each VCPU to completely refresh the tables.  This
> >    request is used for that.
> >  
> > -KVM_REQ_PENDING_TIMER
> > +KVM_REQ_UNBLOCK
> >  
> >    This request may be made from a timer handler run on the host on behalf
> > -  of a VCPU.  It informs the VCPU thread to inject a timer interrupt.
> > +  of a VCPU, or when device assignment is performed. It informs the VCPU to
> > +  exit the vcpu halt inner loop.
> >  
> >  KVM_REQ_UNHALT
> >  
> > Index: kvm/arch/powerpc/include/asm/kvm_host.h
> > ===================================================================
> > --- kvm.orig/arch/powerpc/include/asm/kvm_host.h
> > +++ kvm/arch/powerpc/include/asm/kvm_host.h
> > @@ -51,6 +51,7 @@
> >  /* PPC-specific vcpu->requests bit members */
> >  #define KVM_REQ_WATCHDOG	KVM_ARCH_REQ(0)
> >  #define KVM_REQ_EPR_EXIT	KVM_ARCH_REQ(1)
> > +#define KVM_REQ_PENDING_TIMER	KVM_ARCH_REQ(2)
> >  
> >  #include <linux/mmu_notifier.h>
> >  
> > Index: kvm/arch/x86/kvm/lapic.c
> > ===================================================================
> > --- kvm.orig/arch/x86/kvm/lapic.c
> > +++ kvm/arch/x86/kvm/lapic.c
> > @@ -1657,7 +1657,7 @@ static void apic_timer_expired(struct kv
> >  	}
> >  
> >  	atomic_inc(&apic->lapic_timer.pending);
> > -	kvm_make_request(KVM_REQ_PENDING_TIMER, vcpu);
> > +	kvm_make_request(KVM_REQ_UNBLOCK, vcpu);
> >  	if (from_timer_fn)
> >  		kvm_vcpu_kick(vcpu);
> >  }
> 
> Pure question on the existing code: why do we need kvm_make_request() for
> timer?  As I see kvm_vcpu_check_block() already checks explicitly for timers:
> 
> static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu)
> {
>         ...
> 	if (kvm_cpu_has_pending_timer(vcpu))
> 		goto out;
>         ...
> }
> 
> for x86:
> 
> int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu)
> {
> 	if (lapic_in_kernel(vcpu))
> 		return apic_has_pending_timer(vcpu);
> 
> 	return 0;
> }
> 
> So wondering why we can drop the two references to KVM_REQ_PENDING_TIMER in x86
> directly..

See commit 06e05645661211b9eaadaf6344c335d2e80f0ba2

Re: [patch 2/3] KVM: rename KVM_REQ_PENDING_TIMER to KVM_REQ_UNBLOCK

[Peter Xu]

On Tue, May 25, 2021 at 04:26:37PM -0300, Marcelo Tosatti wrote:
> On Tue, May 25, 2021 at 03:14:33PM -0400, Peter Xu wrote:
> > On Tue, May 25, 2021 at 10:41:17AM -0300, Marcelo Tosatti wrote:
> > > KVM_REQ_UNBLOCK will be used to exit a vcpu from
> > > its inner vcpu halt emulation loop.
> > > 
> > > Rename KVM_REQ_PENDING_TIMER to KVM_REQ_UNBLOCK, switch
> > > PowerPC to arch specific request bit.
> > > 
> > > Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
> > > 
> > > Index: kvm/include/linux/kvm_host.h
> > > ===================================================================
> > > --- kvm.orig/include/linux/kvm_host.h
> > > +++ kvm/include/linux/kvm_host.h
> > > @@ -146,7 +146,7 @@ static inline bool is_error_page(struct
> > >   */
> > >  #define KVM_REQ_TLB_FLUSH         (0 | KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
> > >  #define KVM_REQ_MMU_RELOAD        (1 | KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
> > > -#define KVM_REQ_PENDING_TIMER     2
> > > +#define KVM_REQ_UNBLOCK           2
> > >  #define KVM_REQ_UNHALT            3
> > >  #define KVM_REQUEST_ARCH_BASE     8
> > >  
> > > Index: kvm/virt/kvm/kvm_main.c
> > > ===================================================================
> > > --- kvm.orig/virt/kvm/kvm_main.c
> > > +++ kvm/virt/kvm/kvm_main.c
> > > @@ -2794,6 +2794,8 @@ static int kvm_vcpu_check_block(struct k
> > >  		goto out;
> > >  	if (signal_pending(current))
> > >  		goto out;
> > > +	if (kvm_check_request(KVM_REQ_UNBLOCK, vcpu))
> > > +		goto out;
> > >  
> > >  	ret = 0;
> > >  out:
> > > Index: kvm/Documentation/virt/kvm/vcpu-requests.rst
> > > ===================================================================
> > > --- kvm.orig/Documentation/virt/kvm/vcpu-requests.rst
> > > +++ kvm/Documentation/virt/kvm/vcpu-requests.rst
> > > @@ -118,10 +118,11 @@ KVM_REQ_MMU_RELOAD
> > >    necessary to inform each VCPU to completely refresh the tables.  This
> > >    request is used for that.
> > >  
> > > -KVM_REQ_PENDING_TIMER
> > > +KVM_REQ_UNBLOCK
> > >  
> > >    This request may be made from a timer handler run on the host on behalf
> > > -  of a VCPU.  It informs the VCPU thread to inject a timer interrupt.
> > > +  of a VCPU, or when device assignment is performed. It informs the VCPU to
> > > +  exit the vcpu halt inner loop.
> > >  
> > >  KVM_REQ_UNHALT
> > >  
> > > Index: kvm/arch/powerpc/include/asm/kvm_host.h
> > > ===================================================================
> > > --- kvm.orig/arch/powerpc/include/asm/kvm_host.h
> > > +++ kvm/arch/powerpc/include/asm/kvm_host.h
> > > @@ -51,6 +51,7 @@
> > >  /* PPC-specific vcpu->requests bit members */
> > >  #define KVM_REQ_WATCHDOG	KVM_ARCH_REQ(0)
> > >  #define KVM_REQ_EPR_EXIT	KVM_ARCH_REQ(1)
> > > +#define KVM_REQ_PENDING_TIMER	KVM_ARCH_REQ(2)
> > >  
> > >  #include <linux/mmu_notifier.h>
> > >  
> > > Index: kvm/arch/x86/kvm/lapic.c
> > > ===================================================================
> > > --- kvm.orig/arch/x86/kvm/lapic.c
> > > +++ kvm/arch/x86/kvm/lapic.c
> > > @@ -1657,7 +1657,7 @@ static void apic_timer_expired(struct kv
> > >  	}
> > >  
> > >  	atomic_inc(&apic->lapic_timer.pending);
> > > -	kvm_make_request(KVM_REQ_PENDING_TIMER, vcpu);
> > > +	kvm_make_request(KVM_REQ_UNBLOCK, vcpu);
> > >  	if (from_timer_fn)
> > >  		kvm_vcpu_kick(vcpu);
> > >  }
> > 
> > Pure question on the existing code: why do we need kvm_make_request() for
> > timer?  As I see kvm_vcpu_check_block() already checks explicitly for timers:
> > 
> > static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu)
> > {
> >         ...
> > 	if (kvm_cpu_has_pending_timer(vcpu))
> > 		goto out;
> >         ...
> > }
> > 
> > for x86:
> > 
> > int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu)
> > {
> > 	if (lapic_in_kernel(vcpu))
> > 		return apic_has_pending_timer(vcpu);
> > 
> > 	return 0;
> > }
> > 
> > So wondering why we can drop the two references to KVM_REQ_PENDING_TIMER in x86
> > directly..
> 
> See commit 06e05645661211b9eaadaf6344c335d2e80f0ba2

I see, thanks Marcelo.

Then we might have checked twice on timer pending in kvm_vcpu_check_block() for
x86, as we also checks KVM_REQ_UNBLOCK now. Didn't think further on how to make
it better, e.g. simply dropping kvm_cpu_has_pending_timer() won't work since
it seems to still be useful for non-x86..

Then this patch looks good to me:

Reviewed-by: Peter Xu <peterx@redhat.com>

-- 
Peter Xu

Re: [patch 1/3] KVM: x86: add start_assignment hook to kvm_x86_ops

[Peter Xu]

On Tue, May 25, 2021 at 10:41:16AM -0300, Marcelo Tosatti wrote:
> Add a start_assignment hook to kvm_x86_ops, which is called when 
> kvm_arch_start_assignment is done.
> 
> The hook is required to update the wakeup vector of a sleeping vCPU
> when a device is assigned to the guest.
> 
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

Reviewed-by: Peter Xu <peterx@redhat.com>

-- 
Peter Xu

Re: [patch 3/3] KVM: VMX: update vcpu posted-interrupt descriptor when assigning device

[Peter Xu]

On Tue, May 25, 2021 at 10:41:18AM -0300, Marcelo Tosatti wrote:
> For VMX, when a vcpu enters HLT emulation, pi_post_block will:
> 
> 1) Add vcpu to per-cpu list of blocked vcpus.
> 
> 2) Program the posted-interrupt descriptor "notification vector" 
> to POSTED_INTR_WAKEUP_VECTOR
> 
> With interrupt remapping, an interrupt will set the PIR bit for the 
> vector programmed for the device on the CPU, test-and-set the 
> ON bit on the posted interrupt descriptor, and if the ON bit is clear
> generate an interrupt for the notification vector.
> 
> This way, the target CPU wakes upon a device interrupt and wakes up
> the target vcpu.
> 
> Problem is that pi_post_block only programs the notification vector
> if kvm_arch_has_assigned_device() is true. Its possible for the
> following to happen:
> 
> 1) vcpu V HLTs on pcpu P, kvm_arch_has_assigned_device is false,
> notification vector is not programmed
> 2) device is assigned to VM
> 3) device interrupts vcpu V, sets ON bit
> (notification vector not programmed, so pcpu P remains in idle)
> 4) vcpu 0 IPIs vcpu V (in guest), but since pi descriptor ON bit is set,
> kvm_vcpu_kick is skipped
> 5) vcpu 0 busy spins on vcpu V's response for several seconds, until
> RCU watchdog NMIs all vCPUs.
> 
> To fix this, use the start_assignment kvm_x86_ops callback to kick
> vcpus out of the halt loop, so the notification vector is 
> properly reprogrammed to the wakeup vector.
> 
> Reported-by: Pei Zhang <pezhang@redhat.com>
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
> 
> 
> Index: kvm/arch/x86/kvm/vmx/posted_intr.c
> ===================================================================
> --- kvm.orig/arch/x86/kvm/vmx/posted_intr.c
> +++ kvm/arch/x86/kvm/vmx/posted_intr.c
> @@ -236,6 +236,13 @@ bool pi_has_pending_interrupt(struct kvm
>  		(pi_test_sn(pi_desc) && !pi_is_pir_empty(pi_desc));
>  }
>  
> +void vmx_pi_start_assignment(struct kvm *kvm)
> +{
> +	if (!irq_remapping_cap(IRQ_POSTING_CAP))
> +		return;
> +
> +	kvm_make_all_cpus_request(kvm, KVM_REQ_UNBLOCK);

Shall we add a simple comment block explaining why we need this?

> +}

The patch itself looks right to me.

Reviewed-by: Peter Xu <peterx@redhat.com>

Thanks,

-- 
Peter Xu

Re: [patch 3/3] KVM: VMX: update vcpu posted-interrupt descriptor when assigning device

[kernel test robot]

[-- Attachment #1: Type: text/plain, Size: 1509 bytes --]

Hi Marcelo,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on kvm/queue]
[also build test ERROR on vhost/linux-next v5.13-rc3 next-20210525]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Marcelo-Tosatti/VMX-configure-posted-interrupt-descriptor-when-assigning-device-v5/20210525-215604
base:   https://git.kernel.org/pub/scm/virt/kvm/kvm.git queue
config: x86_64-rhel-8.3 (attached as .config)
compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
reproduce (this is a W=1 build):
        # https://github.com/0day-ci/linux/commit/e515e68f330d3787af0952dcfb3e0fbf2d9b9f06
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Marcelo-Tosatti/VMX-configure-posted-interrupt-descriptor-when-assigning-device-v5/20210525-215604
        git checkout e515e68f330d3787af0952dcfb3e0fbf2d9b9f06
        # save the attached .config to linux build tree
        make W=1 ARCH=x86_64 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>, old ones prefixed by <<):

>> ERROR: modpost: "kvm_make_all_cpus_request" [arch/x86/kvm/kvm-intel.ko] undefined!

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 41426 bytes --]

[patch 3/3 V2] KVM: VMX: update vcpu posted-interrupt descriptor when assigning device

[Marcelo Tosatti]

For VMX, when a vcpu enters HLT emulation, pi_post_block will:

1) Add vcpu to per-cpu list of blocked vcpus.

2) Program the posted-interrupt descriptor "notification vector" 
to POSTED_INTR_WAKEUP_VECTOR

With interrupt remapping, an interrupt will set the PIR bit for the 
vector programmed for the device on the CPU, test-and-set the 
ON bit on the posted interrupt descriptor, and if the ON bit is clear
generate an interrupt for the notification vector.

This way, the target CPU wakes upon a device interrupt and wakes up
the target vcpu.

Problem is that pi_post_block only programs the notification vector
if kvm_arch_has_assigned_device() is true. Its possible for the
following to happen:

1) vcpu V HLTs on pcpu P, kvm_arch_has_assigned_device is false,
notification vector is not programmed
2) device is assigned to VM
3) device interrupts vcpu V, sets ON bit
(notification vector not programmed, so pcpu P remains in idle)
4) vcpu 0 IPIs vcpu V (in guest), but since pi descriptor ON bit is set,
kvm_vcpu_kick is skipped
5) vcpu 0 busy spins on vcpu V's response for several seconds, until
RCU watchdog NMIs all vCPUs.

To fix this, use the start_assignment kvm_x86_ops callback to kick
vcpus out of the halt loop, so the notification vector is 
properly reprogrammed to the wakeup vector.

Reported-by: Pei Zhang <pezhang@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

For build error:
Reported-by: kernel test robot <lkp@intel.com>

---

v2: Add brief comment to vmx_pi_start_assignment (Peter Xu).
    Export kvm_make_all_cpus_request (kernel test robot).


Index: linux-2.6/arch/x86/kvm/vmx/posted_intr.c
===================================================================
--- linux-2.6.orig/arch/x86/kvm/vmx/posted_intr.c
+++ linux-2.6/arch/x86/kvm/vmx/posted_intr.c
@@ -238,6 +238,20 @@ bool pi_has_pending_interrupt(struct kvm
 
 
 /*
+ * Bail out of the block loop if the VM has an assigned
+ * device, but the blocking vCPU didn't reconfigure the
+ * PI.NV to the wakeup vector, i.e. the assigned device
+ * came along after the initial check in pi_pre_block().
+ */
+void vmx_pi_start_assignment(struct kvm *kvm)
+{
+	if (!irq_remapping_cap(IRQ_POSTING_CAP))
+		return;
+
+	kvm_make_all_cpus_request(kvm, KVM_REQ_UNBLOCK);
+}
+
+/*
  * pi_update_irte - set IRTE for Posted-Interrupts
  *
  * @kvm: kvm
Index: linux-2.6/arch/x86/kvm/vmx/posted_intr.h
===================================================================
--- linux-2.6.orig/arch/x86/kvm/vmx/posted_intr.h
+++ linux-2.6/arch/x86/kvm/vmx/posted_intr.h
@@ -95,5 +95,6 @@ void __init pi_init_cpu(int cpu);
 bool pi_has_pending_interrupt(struct kvm_vcpu *vcpu);
 int pi_update_irte(struct kvm *kvm, unsigned int host_irq, uint32_t guest_irq,
 		   bool set);
+void vmx_pi_start_assignment(struct kvm *kvm);
 
 #endif /* __KVM_X86_VMX_POSTED_INTR_H */
Index: linux-2.6/arch/x86/kvm/vmx/vmx.c
===================================================================
--- linux-2.6.orig/arch/x86/kvm/vmx/vmx.c
+++ linux-2.6/arch/x86/kvm/vmx/vmx.c
@@ -7732,6 +7732,7 @@ static struct kvm_x86_ops vmx_x86_ops __
 	.nested_ops = &vmx_nested_ops,
 
 	.update_pi_irte = pi_update_irte,
+	.start_assignment = vmx_pi_start_assignment,
 
 #ifdef CONFIG_X86_64
 	.set_hv_timer = vmx_set_hv_timer,
Index: linux-2.6/virt/kvm/kvm_main.c
===================================================================
--- linux-2.6.orig/virt/kvm/kvm_main.c
+++ linux-2.6/virt/kvm/kvm_main.c
@@ -307,6 +307,7 @@ bool kvm_make_all_cpus_request(struct kv
 {
 	return kvm_make_all_cpus_request_except(kvm, req, NULL);
 }
+EXPORT_SYMBOL_GPL(kvm_make_all_cpus_request);
 
 #ifndef CONFIG_HAVE_KVM_ARCH_TLB_FLUSH_ALL
 void kvm_flush_remote_tlbs(struct kvm *kvm)

Re: [patch 2/3] KVM: rename KVM_REQ_PENDING_TIMER to KVM_REQ_UNBLOCK

[Paolo Bonzini]

On 25/05/21 21:52, Peter Xu wrote:
> Didn't think further on how to make it better, e.g. simply dropping
> kvm_cpu_has_pending_timer() won't work since it seems to still be
> useful for non-x86..

It should be possible to use KVM_REQ_UNBLOCK in other architectures, and
drop kvm_cpu_has_pending_timer().

Paolo

Re: [patch 2/3] KVM: rename KVM_REQ_PENDING_TIMER to KVM_REQ_UNBLOCK

[Paolo Bonzini]

On 25/05/21 15:41, Marcelo Tosatti wrote:
> -KVM_REQ_PENDING_TIMER
> +KVM_REQ_UNBLOCK
>   
>     This request may be made from a timer handler run on the host on behalf
> -  of a VCPU.  It informs the VCPU thread to inject a timer interrupt.
> +  of a VCPU, or when device assignment is performed. It informs the VCPU to
> +  exit the vcpu halt inner loop.
>   

A small change:

   This request informs the vCPU to exit kvm_vcpu_block.  It is used for
   example from timer handlers that run on the host on behalf of a vCPU,
   or in order to update the interrupt routing and ensure that assigned
   devices will wake up the vCPU.

Paolo

Re: [patch 0/3] VMX: configure posted interrupt descriptor when assigning device (v5)

[Paolo Bonzini]

On 25/05/21 15:41, Marcelo Tosatti wrote:
> Configuration of the posted interrupt descriptor is incorrect when devices
> are hotplugged to the guest (and vcpus are halted).
> 
> See patch 3 for details.
> 
> ---
> 
> v5: use KVM_REQ_UNBLOCK instead of kvm_check_block callback (Paolo / Peter Xu)
> 
> v4: remove NULL assignments from kvm_x86_ops (Peter Xu)
>      check for return value of ->start_assignment directly (Peter Xu)
> 
> v3: improved comments (Sean)
>      use kvm_vcpu_wake_up (Sean)
>      drop device_count from start_assignment function (Peter Xu)
> 
> v2: rather than using a potentially racy IPI (vs vcpu->cpu switches),
>      kick the vcpus when assigning a device and let the blocked per-CPU
>      list manipulation happen locally at ->pre_block and ->post_block
>      (Sean Christopherson).
> 
> 
> 

Queued, thanks.

Paolo