Re: [PATCH v3 1/3] KVM: Implement dirty quota-based throttling of vcpus

[Sean Christopherson <seanjc@google.com>]

This whole series needs to be Cc'd to the arm64 and s390 folks.  The easiest way
to that is to use scripts/get_maintainers.pl, which will grab the appropriate
people.  There are a variety of options you can use to tailor it to your style.
E.g. for KVM I do

  --nogit --nogit-fallback --norolestats --nofixes --pattern-depth=1

for To:, and then add

  --nom

for Cc:.  The --pattern-depth=1 tells it to not recurse up so that it doesn't
include the x86 maintainers for arch/x86/kvm patches.

I'd Cc them manually, but I think it'll be easier to just post v4.

On Sun, Mar 06, 2022, Shivam Kumar wrote:
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index eb4029660bd9..0b35b8cc0274 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10257,6 +10257,10 @@ static int vcpu_run(struct kvm_vcpu *vcpu)
>  	vcpu->arch.l1tf_flush_l1d = true;
>  
>  	for (;;) {
> +		r = kvm_vcpu_check_dirty_quota(vcpu);
> +		if (!r)
> +			break;
> +
>  		if (kvm_vcpu_running(vcpu)) {
>  			r = vcpu_enter_guest(vcpu);
>  		} else {
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index f11039944c08..b1c599c78c42 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -530,6 +530,21 @@ static inline int kvm_vcpu_exiting_guest_mode(struct kvm_vcpu *vcpu)
>  	return cmpxchg(&vcpu->mode, IN_GUEST_MODE, EXITING_GUEST_MODE);
>  }
>  
> +static inline int kvm_vcpu_check_dirty_quota(struct kvm_vcpu *vcpu)
> +{
> +	u64 dirty_quota = READ_ONCE(vcpu->run->dirty_quota);
> +	u64 pages_dirtied = vcpu->stat.generic.pages_dirtied;
> +	struct kvm_run *run = vcpu->run;

Might as well use "run" when reading the dirty quota.

> +
> +	if (!dirty_quota || (pages_dirtied < dirty_quota))
> +		return 1;

I don't love returning 0/1 from a function that suggests it returns a bool, but
I do agree it's better than actually returning a bool.  I also don't have a better
name, so I'm just whining in the hope that Paolo or someone else has an idea :-)

> +	run->exit_reason = KVM_EXIT_DIRTY_QUOTA_EXHAUSTED;
> +	run->dirty_quota_exit.count = pages_dirtied;
> +	run->dirty_quota_exit.quota = dirty_quota;
> +	return 0;
> +}