Re: [PATCH 1/7] KVM: arm64: Add two page mapping counters for kvm_stat

From: Keqian Zhu <zhukeqian1@huawei.com>
To: Yoan Picchi <yoan.picchi@arm.com>, <maz@kernel.org>,
	<james.morse@arm.com>, <julien.thierry.kdev@gmail.com>,
	<suzuki.poulose@arm.com>, <linux-arm-kernel@lists.infradead.org>,
	<kvmarm@lists.cs.columbia.edu>
Cc: <catalin.marinas@arm.com>, <will@kernel.org>
Subject: Re: [PATCH 1/7] KVM: arm64: Add two page mapping counters for kvm_stat
Date: Tue, 23 Mar 2021 19:52:38 +0800	[thread overview]
Message-ID: <fe120fea-b2a3-d80f-38df-2430a0b2029e@huawei.com> (raw)
In-Reply-To: <20210319161711.24972-2-yoan.picchi@arm.com>

Hi Yoan,

On 2021/3/20 0:17, Yoan Picchi wrote:
> Add a counter for when a regular page is mapped, and another
> for when a huge page is mapped.
> 
> Signed-off-by: Yoan Picchi <yoan.picchi@arm.com>
> ---
>  arch/arm64/include/asm/kvm_host.h | 2 ++
>  arch/arm64/kvm/guest.c            | 2 ++
>  arch/arm64/kvm/mmu.c              | 7 +++++++
>  3 files changed, 11 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 3d10e6527..863603285 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -561,6 +561,8 @@ struct kvm_vcpu_stat {
>  	u64 wfi_exit_stat;
>  	u64 mmio_exit_user;
>  	u64 mmio_exit_kernel;
> +	u64 regular_page_mapped;
> +	u64 huge_page_mapped;
>  	u64 exits;
>  };
>  
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index 9bbd30e62..14b15fb8f 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -38,6 +38,8 @@ struct kvm_stats_debugfs_item debugfs_entries[] = {
>  	VCPU_STAT("wfi_exit_stat", wfi_exit_stat),
>  	VCPU_STAT("mmio_exit_user", mmio_exit_user),
>  	VCPU_STAT("mmio_exit_kernel", mmio_exit_kernel),
> +	VCPU_STAT("regular_page_mapped", regular_page_mapped),
> +	VCPU_STAT("huge_page_mapped", huge_page_mapped),
>  	VCPU_STAT("exits", exits),
>  	VCPU_STAT("halt_poll_success_ns", halt_poll_success_ns),
>  	VCPU_STAT("halt_poll_fail_ns", halt_poll_fail_ns),
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 77cb2d28f..3996b28da 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -914,6 +914,13 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>  		mark_page_dirty(kvm, gfn);
>  	}
>  
> +	if (ret >= 0) {
> +		if (vma_pagesize == PAGE_SIZE) {
> +			vcpu->stat.regular_page_mapped++;
> +		} else {
> +			vcpu->stat.huge_page_mapped++;
> +		}
> +	}
This looks too simple, as we don't always map a new regular_page or huge_page here.
We may just relax permission or change mapping size, etc. If we mix these operations,
the stat result seems not very valuable...

Thanks,
Keqian

>  out_unlock:
>  	spin_unlock(&kvm->mmu_lock);
>  	kvm_set_pfn_accessed(pfn);
> 

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