Re: [PATCH RFC 1/2] KVM: s390: vsie: simulate VCPU SIE entry/exit

[Pierre Morel <pmorel@linux.ibm.com>]

On 07/08/2018 14:51, David Hildenbrand wrote:
> VCPU requests and VCPU blocking right now don't take care of the vSIE
> (as it was not necessary until now). But we want to have VCPU requests
> that will also be handled before running the vSIE again.
>
> So let's simulate a SIE entry when entering the vSIE loop and check
> for PROG_ flags. The existing infrastructure (e.g. exit_sie()) will then
> detect that the SIE (in form of the vSIE execution loop) is running and
> properly kick the vSIE CPU, resulting in it leaving the vSIE loop and
> therefore the vSIE interception handler, allowing it to handle VCPU
> requests.
>
> E.g. if we want to modify the crycb of the VCPU and make sure that any
> masks also get applied to the VSIE crycb shadow (which uses masks from the
> VCPU crycb), we will need a way to hinder the vSIE from running and make
> sure to process the updated crycb before reentering the vSIE again.
>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>   arch/s390/kvm/kvm-s390.c |  9 ++++++++-
>   arch/s390/kvm/kvm-s390.h |  1 +
>   arch/s390/kvm/vsie.c     | 20 ++++++++++++++++++--
>   3 files changed, 27 insertions(+), 3 deletions(-)
>
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 91ad4a9425c0..c87734a31fdb 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -2766,18 +2766,25 @@ static void kvm_s390_vcpu_request(struct kvm_vcpu *vcpu)
>   	exit_sie(vcpu);
>   }
>   
> +bool kvm_s390_vcpu_sie_inhibited(struct kvm_vcpu *vcpu)
> +{
> +	return atomic_read(&vcpu->arch.sie_block->prog20) &
> +	       (PROG_BLOCK_SIE | PROG_REQUEST);
> +}
> +
>   static void kvm_s390_vcpu_request_handled(struct kvm_vcpu *vcpu)
>   {
>   	atomic_andnot(PROG_REQUEST, &vcpu->arch.sie_block->prog20);
>   }
>   
>   /*
> - * Kick a guest cpu out of SIE and wait until SIE is not running.
> + * Kick a guest cpu out of (v)SIE and wait until (v)SIE is not running.
>    * If the CPU is not running (e.g. waiting as idle) the function will
>    * return immediately. */
>   void exit_sie(struct kvm_vcpu *vcpu)
>   {
>   	kvm_s390_set_cpuflags(vcpu, CPUSTAT_STOP_INT);
> +	kvm_s390_vsie_kick(vcpu);
>   	while (vcpu->arch.sie_block->prog0c & PROG_IN_SIE)
>   		cpu_relax();
>   }
> diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h
> index 981e3ba97461..1f6e36cdce0d 100644
> --- a/arch/s390/kvm/kvm-s390.h
> +++ b/arch/s390/kvm/kvm-s390.h
> @@ -290,6 +290,7 @@ void kvm_s390_vcpu_start(struct kvm_vcpu *vcpu);
>   void kvm_s390_vcpu_stop(struct kvm_vcpu *vcpu);
>   void kvm_s390_vcpu_block(struct kvm_vcpu *vcpu);
>   void kvm_s390_vcpu_unblock(struct kvm_vcpu *vcpu);
> +bool kvm_s390_vcpu_sie_inhibited(struct kvm_vcpu *vcpu);
>   void exit_sie(struct kvm_vcpu *vcpu);
>   void kvm_s390_sync_request(int req, struct kvm_vcpu *vcpu);
>   int kvm_s390_vcpu_setup_cmma(struct kvm_vcpu *vcpu);
> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
> index 63844b95c22c..faac06886f77 100644
> --- a/arch/s390/kvm/vsie.c
> +++ b/arch/s390/kvm/vsie.c
> @@ -989,6 +989,17 @@ static int vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
>   	struct kvm_s390_sie_block *scb_s = &vsie_page->scb_s;
>   	int rc = 0;
>   
> +	/*
> +	 * Simulate a SIE entry of the VCPU (see sie64a), so VCPU blocking
> +	 * and VCPU requests can hinder the whole vSIE loop from running
> +	 * and lead to an immediate exit. We do it at this point (not
> +	 * earlier), so kvm_s390_vsie_kick() works correctly already.
> +	 */
> +	vcpu->arch.sie_block->prog0c |= PROG_IN_SIE;
> +	barrier();
> +	if (kvm_s390_vcpu_sie_inhibited(vcpu))
> +		return 0;
> +
>   	while (1) {
>   		rc = acquire_gmap_shadow(vcpu, vsie_page);
>   		if (!rc)
> @@ -1004,10 +1015,14 @@ static int vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
>   		if (rc == -EAGAIN)
>   			rc = 0;
>   		if (rc || scb_s->icptcode || signal_pending(current) ||
> -		    kvm_s390_vcpu_has_irq(vcpu, 0))
> +		    kvm_s390_vcpu_has_irq(vcpu, 0) ||
> +		    kvm_s390_vcpu_sie_inhibited(vcpu))
>   			break;
>   	}
>   
> +	barrier();
> +	vcpu->arch.sie_block->prog0c &= ~PROG_IN_SIE;
> +
>   	if (rc == -EFAULT) {
>   		/*
>   		 * Addressing exceptions are always presentes as intercepts.
> @@ -1121,7 +1136,8 @@ int kvm_s390_handle_vsie(struct kvm_vcpu *vcpu)
>   	if (unlikely(scb_addr & 0x1ffUL))
>   		return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);
>   
> -	if (signal_pending(current) || kvm_s390_vcpu_has_irq(vcpu, 0))
> +	if (signal_pending(current) || kvm_s390_vcpu_has_irq(vcpu, 0) ||
> +	    kvm_s390_vcpu_sie_inhibited(vcpu))
>   		return 0;
>   
>   	vsie_page = get_vsie_page(vcpu->kvm, scb_addr);

Reviewed-by: Pierre Morel<pmorel@linux.ibm.com>
Tested-by: Pierre Morel<pmorel@linux.ibm.com>

-- 
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany