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 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