Re: [PATCH v5 4/4] KVM: arm64/mmu: count KVM s2 mmu usage in secondary pagetable stats

[Oliver Upton <oliver.upton@linux.dev>]

Hi Yosry,

On Mon, Jun 06, 2022 at 10:20:58PM +0000, Yosry Ahmed wrote:
> Count the pages used by KVM in arm64 for stage2 mmu in secondary pagetable
> stats.

You could probably benefit from being a bit more verbose in the commit
message here as well, per Sean's feedback.

> Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
> ---
>  arch/arm64/kvm/mmu.c | 36 ++++++++++++++++++++++++++++++++----
>  1 file changed, 32 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index f5651a05b6a85..80bc92601fd96 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -92,9 +92,13 @@ static bool kvm_is_device_pfn(unsigned long pfn)
>  static void *stage2_memcache_zalloc_page(void *arg)
>  {
>  	struct kvm_mmu_memory_cache *mc = arg;
> +	void *virt;
>  
>  	/* Allocated with __GFP_ZERO, so no need to zero */
> -	return kvm_mmu_memory_cache_alloc(mc);
> +	virt = kvm_mmu_memory_cache_alloc(mc);
> +	if (virt)
> +		kvm_account_pgtable_pages(virt, 1);
> +	return virt;
>  }
>  
>  static void *kvm_host_zalloc_pages_exact(size_t size)
> @@ -102,6 +106,21 @@ static void *kvm_host_zalloc_pages_exact(size_t size)
>  	return alloc_pages_exact(size, GFP_KERNEL_ACCOUNT | __GFP_ZERO);
>  }
>  
> +static void *kvm_s2_zalloc_pages_exact(size_t size)
> +{
> +	void *virt = kvm_host_zalloc_pages_exact(size);
> +
> +	if (virt)
> +		kvm_account_pgtable_pages(virt, (size >> PAGE_SHIFT));
> +	return virt;
> +}
> +
> +static void kvm_s2_free_pages_exact(void *virt, size_t size)
> +{
> +	kvm_account_pgtable_pages(virt, -(size >> PAGE_SHIFT));
> +	free_pages_exact(virt, size);
> +}
> +
>  static void kvm_host_get_page(void *addr)
>  {
>  	get_page(virt_to_page(addr));
> @@ -112,6 +131,15 @@ static void kvm_host_put_page(void *addr)
>  	put_page(virt_to_page(addr));
>  }
>  
> +static void kvm_s2_put_page(void *addr)
> +{
> +	struct page *p = virt_to_page(addr);
> +	/* Dropping last refcount, the page will be freed */
> +	if (page_count(p) == 1)
> +		kvm_account_pgtable_pages(addr, -1);
> +	put_page(p);

Probably more of a note to myself with the parallel fault series, but
this is a race waiting to happen. This only works because stage 2 pages
are dropped behind the write lock.

Besides the commit message nit:

Reviewed-by: Oliver Upton <oliver.upton@linux.dev>