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

[Peter Xu <peterx@redhat.com>]

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