Re: [PATCH 3/3] kvm-s390: streamline memslot handling

[Avi Kivity <avi@redhat.com>]

ehrhardt@linux.vnet.ibm.com wrote:
> From: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>
>
> This patch relocates the variables kvm-s390 uses to track guest mem addr/size.
> As discussed dropping the variables at struct kvm_arch level allows to use the
> common vcpu->request based mechanism to reload guest memory if e.g. changes
> via set_memory_region.
> The kick mechanism introduced in this series is used to ensure running vcpus
> leave guest state to catch the update.
>
>
>   
>
>  rerun_vcpu:
> +	if (vcpu->requests)
> +		if (test_and_clear_bit(KVM_REQ_MMU_RELOAD, &vcpu->requests))
> +			kvm_s390_vcpu_set_mem(vcpu);
> +
>  	/* verify, that memory has been registered */
> -	if (!vcpu->kvm->arch.guest_memsize) {
> +	if (!vcpu->arch.sie_block->gmslm) {
>  		vcpu_put(vcpu);
> +		VCPU_EVENT(vcpu, 3, "%s", "no memory registered to run vcpu");
>  		return -EINVAL;
>  	}


x86 uses a double check: first we check vcpu->requests outside atomic 
context, then we enter the critical section and check again for signals 
and vcpu->requests.

This allows us (a) to do naughty things in vcpu->requests handlers, (b) 
keep the critical section short.

Does this apply here?

> -	/* update sie control blocks, and unlock all vcpus */
> +	/* request update of sie control block for all available vcpus */
>  	for (i = 0; i < KVM_MAX_VCPUS; ++i) {
>  		if (kvm->vcpus[i]) {
> -			kvm->vcpus[i]->arch.sie_block->gmsor =
> -				kvm->arch.guest_origin;
> -			kvm->vcpus[i]->arch.sie_block->gmslm =
> -				kvm->arch.guest_memsize +
> -				kvm->arch.guest_origin +
> -				VIRTIODESCSPACE - 1ul;
> -			mutex_unlock(&kvm->vcpus[i]->mutex);
> +			set_bit(KVM_REQ_MMU_RELOAD, &kvm->vcpus[i]->requests);
> +			kvm_s390_inject_sigp_stop(kvm->vcpus[i],
> +						  ACTION_RELOADVCPU_ON_STOP);
>  		}
>  	}
>   

There already exists a loop which does this, see 
make_all_cpus_request().  It uses an IPI (Marcelo, can't it use the 
reschedule interrupt?).  It has a couple of optimizations -- if the 
request is already set, it skips the IPI, and it avoids the IPI for 
vcpus out of guest mode.  Maybe it could fit s390 too.


-- 
error compiling committee.c: too many arguments to function