Re: [PATCH v8 3/3] KVM: arm64: Dirty quota-based throttling of vcpus

[Marc Zyngier <maz@kernel.org>]

On Sat, 25 Feb 2023 20:48:01 +0000,
Shivam Kumar <shivam.kumar1@nutanix.com> wrote:
> 
> Call update_dirty_quota whenever a page is marked dirty with
> appropriate arch-specific page size. Process the KVM request
> KVM_REQ_DIRTY_QUOTA_EXIT (raised by update_dirty_quota) to exit to
> userspace with exit reason KVM_EXIT_DIRTY_QUOTA_EXHAUSTED.
> 
> Suggested-by: Shaju Abraham <shaju.abraham@nutanix.com>
> Suggested-by: Manish Mishra <manish.mishra@nutanix.com>
> Co-developed-by: Anurag Madnawat <anurag.madnawat@nutanix.com>
> Signed-off-by: Anurag Madnawat <anurag.madnawat@nutanix.com>
> Signed-off-by: Shivam Kumar <shivam.kumar1@nutanix.com>
> ---
>  arch/arm64/kvm/Kconfig | 1 +
>  arch/arm64/kvm/arm.c   | 7 +++++++
>  arch/arm64/kvm/mmu.c   | 3 +++
>  3 files changed, 11 insertions(+)
> 
> diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
> index ca6eadeb7d1a..8e7dea2c3a9f 100644
> --- a/arch/arm64/kvm/Kconfig
> +++ b/arch/arm64/kvm/Kconfig
> @@ -44,6 +44,7 @@ menuconfig KVM
>  	select SCHED_INFO
>  	select GUEST_PERF_EVENTS if PERF_EVENTS
>  	select INTERVAL_TREE
> +	select HAVE_KVM_DIRTY_QUOTA

So this is selected unconditionally...

>  	help
>  	  Support hosting virtualized guest machines.
>  
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 3bd732eaf087..5162b2fc46a1 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -757,6 +757,13 @@ static int check_vcpu_requests(struct kvm_vcpu *vcpu)
>  
>  		if (kvm_dirty_ring_check_request(vcpu))
>  			return 0;
> +
> +#ifdef CONFIG_HAVE_KVM_DIRTY_QUOTA

... and yet you litter the arch code with #ifdefs...

> +		if (kvm_check_request(KVM_REQ_DIRTY_QUOTA_EXIT, vcpu)) {
> +			vcpu->run->exit_reason = KVM_EXIT_DIRTY_QUOTA_EXHAUSTED;
> +			return 0;

What rechecks the quota on entry?

> +		}
> +#endif
>  	}
>  
>  	return 1;
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 7113587222ff..baf416046f46 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -1390,6 +1390,9 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>  	/* Mark the page dirty only if the fault is handled successfully */
>  	if (writable && !ret) {
>  		kvm_set_pfn_dirty(pfn);
> +#ifdef CONFIG_HAVE_KVM_DIRTY_QUOTA
> +		update_dirty_quota(kvm, fault_granule);

fault_granule isn't necessarily the amount that gets dirtied.

	M.

-- 
Without deviation from the norm, progress is not possible.