Subject: Re: [PATCH 5/7] KVM: arm64: Remove hyp_pool pointer from struct hyp_page

From: Marc Zyngier <[email-masked]>
Date: Tue, 01 Jun 2021 16:00:04 +0100

On Thu, 27 May 2021 13:51:32 +0100,
Quentin Perret <[email-masked]> wrote:
> 
> Each struct hyp_page currently contains a pointer to a hyp_pool struct
> where the page should be freed if its refcount reaches 0. However, this
> information can always be inferred from the context in the EL2 code, so
> drop the pointer to save a few bytes in the vmemmap.
> 
> Signed-off-by: Quentin Perret <[email-masked]>
> ---
>  arch/arm64/kvm/hyp/include/nvhe/gfp.h    |  4 ++--
>  arch/arm64/kvm/hyp/include/nvhe/memory.h |  2 --
>  arch/arm64/kvm/hyp/nvhe/mem_protect.c    | 13 +++++++++++--
>  arch/arm64/kvm/hyp/nvhe/page_alloc.c     |  7 ++-----
>  arch/arm64/kvm/hyp/nvhe/setup.c          | 14 ++++++++++++--
>  5 files changed, 27 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/include/nvhe/gfp.h b/arch/arm64/kvm/hyp/include/nvhe/gfp.h
> index aada4d97de49..9ed374648364 100644
> --- a/arch/arm64/kvm/hyp/include/nvhe/gfp.h
> +++ b/arch/arm64/kvm/hyp/include/nvhe/gfp.h
> @@ -42,8 +42,8 @@ static inline void hyp_set_page_refcounted(struct hyp_page *p)
>  
>  /* Allocation */
>  void *hyp_alloc_pages(struct hyp_pool *pool, unsigned int order);
> -void hyp_get_page(void *addr);
> -void hyp_put_page(void *addr);
> +void hyp_get_page(void *addr, struct hyp_pool *pool);
> +void hyp_put_page(void *addr, struct hyp_pool *pool);

It'd be good to be consistent with __hyp_put_page(), which has these
arguments in the opposite order. See below for an example.

>  
>  /* Used pages cannot be freed */
>  int hyp_pool_init(struct hyp_pool *pool, u64 pfn, unsigned int nr_pages,
> diff --git a/arch/arm64/kvm/hyp/include/nvhe/memory.h b/arch/arm64/kvm/hyp/include/nvhe/memory.h
> index 7691ab495eb4..991636be2f46 100644
> --- a/arch/arm64/kvm/hyp/include/nvhe/memory.h
> +++ b/arch/arm64/kvm/hyp/include/nvhe/memory.h
> @@ -7,11 +7,9 @@
>  
>  #include <linux/types.h>
>  
> -struct hyp_pool;
>  struct hyp_page {
>  	unsigned int refcount;
>  	unsigned int order;
> -	struct hyp_pool *pool;
>  };
>  
>  extern u64 __hyp_vmemmap;
> diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> index fdd5b5702e8a..3603311eb41c 100644
> --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> @@ -42,6 +42,15 @@ static void *host_s2_zalloc_page(void *pool)
>  {
>  	return hyp_alloc_pages(pool, 0);
>  }
> +static void host_s2_get_page(void *addr)

nit: missing blank line.

> +{
> +	hyp_get_page(addr, &host_s2_pool);
> +}
> +
> +static void host_s2_put_page(void *addr)
> +{
> +	hyp_put_page(addr, &host_s2_pool);
> +}
>  
>  static int prepare_s2_pool(void *pgt_pool_base)
>  {
> @@ -60,8 +69,8 @@ static int prepare_s2_pool(void *pgt_pool_base)
>  		.phys_to_virt = hyp_phys_to_virt,
>  		.virt_to_phys = hyp_virt_to_phys,
>  		.page_count = hyp_page_count,
> -		.get_page = hyp_get_page,
> -		.put_page = hyp_put_page,
> +		.get_page = host_s2_get_page,
> +		.put_page = host_s2_put_page,
>  	};
>  
>  	return 0;
> diff --git a/arch/arm64/kvm/hyp/nvhe/page_alloc.c b/arch/arm64/kvm/hyp/nvhe/page_alloc.c
> index ce7379f1480b..e453108a2d95 100644
> --- a/arch/arm64/kvm/hyp/nvhe/page_alloc.c
> +++ b/arch/arm64/kvm/hyp/nvhe/page_alloc.c
> @@ -150,20 +150,18 @@ static void __hyp_put_page(struct hyp_pool *pool, struct hyp_page *p)
>  		__hyp_attach_page(pool, p);
>  }
>  
> -void hyp_put_page(void *addr)
> +void hyp_put_page(void *addr, struct hyp_pool *pool)
>  {
>  	struct hyp_page *p = hyp_virt_to_page(addr);
> -	struct hyp_pool *pool = hyp_page_to_pool(p);
>  
>  	hyp_spin_lock(&pool->lock);
>  	__hyp_put_page(pool, p);

When I see this, my eyes get crossed, and I don't know what I'm
reading anymore! ;-) In general, I like the "container" as a first
argument, followed by the element that can be contained.

>  	hyp_spin_unlock(&pool->lock);
>  }
>  
> -void hyp_get_page(void *addr)
> +void hyp_get_page(void *addr, struct hyp_pool *pool)
>  {
>  	struct hyp_page *p = hyp_virt_to_page(addr);
> -	struct hyp_pool *pool = hyp_page_to_pool(p);
>  
>  	hyp_spin_lock(&pool->lock);
>  	hyp_page_ref_inc(p);
> @@ -212,7 +210,6 @@ int hyp_pool_init(struct hyp_pool *pool, u64 pfn, unsigned int nr_pages,
>  	/* Init the vmemmap portion */
>  	p = hyp_phys_to_page(phys);
>  	for (i = 0; i < nr_pages; i++) {
> -		p[i].pool = pool;
>  		p[i].order = 0;
>  		hyp_set_page_refcounted(&p[i]);
>  	}
> diff --git a/arch/arm64/kvm/hyp/nvhe/setup.c b/arch/arm64/kvm/hyp/nvhe/setup.c
> index 709cb3d19eb7..bf61abd4a330 100644
> --- a/arch/arm64/kvm/hyp/nvhe/setup.c
> +++ b/arch/arm64/kvm/hyp/nvhe/setup.c
> @@ -137,6 +137,16 @@ static void *hyp_zalloc_hyp_page(void *arg)
>  	return hyp_alloc_pages(&hpool, 0);
>  }
>  
> +static void hpool_get_page(void *addr)
> +{
> +	hyp_get_page(addr, &hpool);
> +}
> +
> +static void hpool_put_page(void *addr)
> +{
> +	hyp_put_page(addr, &hpool);
> +}
> +
>  void __noreturn __pkvm_init_finalise(void)
>  {
>  	struct kvm_host_data *host_data = this_cpu_ptr(&kvm_host_data);
> @@ -160,8 +170,8 @@ void __noreturn __pkvm_init_finalise(void)
>  		.zalloc_page = hyp_zalloc_hyp_page,
>  		.phys_to_virt = hyp_phys_to_virt,
>  		.virt_to_phys = hyp_virt_to_phys,
> -		.get_page = hyp_get_page,
> -		.put_page = hyp_put_page,
> +		.get_page = hpool_get_page,
> +		.put_page = hpool_put_page,
>  	};
>  	pkvm_pgtable.mm_ops = &pkvm_pgtable_mm_ops;
>  
> -- 
> 2.31.1.818.g46aad6cb9e-goog
> 
> 

Thanks,

	M.

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

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