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Date: Wed, 10 Apr 2024 19:42:36 +0200
From: Claudio Imbrenda <imbrenda@linux.ibm.com>
To: David Hildenbrand <david@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linux-s390@vger.kernel.org, kvm@vger.kernel.org,
        Matthew Wilcox
 <willy@infradead.org>,
        Heiko Carstens <hca@linux.ibm.com>, Vasily Gorbik
 <gor@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        Christian
 Borntraeger <borntraeger@linux.ibm.com>,
        Sven Schnelle
 <svens@linux.ibm.com>,
        Janosch Frank <frankja@linux.ibm.com>,
        Gerald
 Schaefer <gerald.schaefer@linux.ibm.com>,
        Thomas Huth <thuth@redhat.com>
Subject: Re: [PATCH v1 3/5] s390/uv: convert PG_arch_1 users to only work on
 small folios
Message-ID: <20240410194236.1c89eb7d@p-imbrenda>
In-Reply-To: <20240404163642.1125529-4-david@redhat.com>
References: <20240404163642.1125529-1-david@redhat.com>
	<20240404163642.1125529-4-david@redhat.com>
Organization: IBM
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On Thu,  4 Apr 2024 18:36:40 +0200
David Hildenbrand <david@redhat.com> wrote:

> Now that make_folio_secure() may only set PG_arch_1 for small folios,
> let's convert relevant remaining UV code to only work on (small) folios
> and simply reject large folios early. This way, we'll never end up
> touching PG_arch_1 on tail pages of a large folio in UV code.
> 
> The folio_get()/folio_put() for functions that are documented to already
> hold a folio reference look weird and it should probably be removed.
> Similarly, uv_destroy_owned_page() and uv_convert_owned_from_secure()
> should really consume a folio reference instead. But these are cleanups for
> another day.
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  arch/s390/include/asm/page.h |  1 +
>  arch/s390/kernel/uv.c        | 39 +++++++++++++++++++++---------------
>  2 files changed, 24 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/s390/include/asm/page.h b/arch/s390/include/asm/page.h
> index 54d015bcd8e3..b64384872c0f 100644
> --- a/arch/s390/include/asm/page.h
> +++ b/arch/s390/include/asm/page.h
> @@ -214,6 +214,7 @@ static inline unsigned long __phys_addr(unsigned long x, bool is_31bit)
>  #define pfn_to_phys(pfn)	((pfn) << PAGE_SHIFT)
>  
>  #define phys_to_page(phys)	pfn_to_page(phys_to_pfn(phys))
> +#define phys_to_folio(phys)	page_folio(phys_to_page(phys))
>  #define page_to_phys(page)	pfn_to_phys(page_to_pfn(page))
>  #define folio_to_phys(page)	pfn_to_phys(folio_pfn(folio))
>  
> diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
> index adcbd4b13035..9c0113b26735 100644
> --- a/arch/s390/kernel/uv.c
> +++ b/arch/s390/kernel/uv.c
> @@ -134,14 +134,17 @@ static int uv_destroy_page(unsigned long paddr)
>   */
>  int uv_destroy_owned_page(unsigned long paddr)
>  {
> -	struct page *page = phys_to_page(paddr);
> +	struct folio *folio = phys_to_folio(paddr);
>  	int rc;
>  
> -	get_page(page);
> +	if (unlikely(folio_test_large(folio)))
> +		return 0;

please add a comment here to explain why it's ok to just return 0
here...

> +
> +	folio_get(folio);
>  	rc = uv_destroy_page(paddr);
>  	if (!rc)
> -		clear_bit(PG_arch_1, &page->flags);
> -	put_page(page);
> +		clear_bit(PG_arch_1, &folio->flags);
> +	folio_put(folio);
>  	return rc;
>  }
>  
> @@ -169,14 +172,17 @@ int uv_convert_from_secure(unsigned long paddr)
>   */
>  int uv_convert_owned_from_secure(unsigned long paddr)
>  {
> -	struct page *page = phys_to_page(paddr);
> +	struct folio *folio = phys_to_folio(paddr);
>  	int rc;
>  
> -	get_page(page);
> +	if (unlikely(folio_test_large(folio)))
> +		return 0;

.. and here

> +
> +	folio_get(folio);
>  	rc = uv_convert_from_secure(paddr);
>  	if (!rc)
> -		clear_bit(PG_arch_1, &page->flags);
> -	put_page(page);
> +		clear_bit(PG_arch_1, &folio->flags);
> +	folio_put(folio);
>  	return rc;
>  }
>  
> @@ -457,33 +463,34 @@ EXPORT_SYMBOL_GPL(gmap_destroy_page);
>   */
>  int arch_make_page_accessible(struct page *page)
>  {
> +	struct folio *folio = page_folio(page);
>  	int rc = 0;
>  
> -	/* Hugepage cannot be protected, so nothing to do */
> -	if (PageHuge(page))
> +	/* Large folios cannot be protected, so nothing to do */
> +	if (unlikely(folio_test_large(folio)))
>  		return 0;
>  
>  	/*
>  	 * PG_arch_1 is used in 3 places:
>  	 * 1. for kernel page tables during early boot
>  	 * 2. for storage keys of huge pages and KVM
> -	 * 3. As an indication that this page might be secure. This can
> +	 * 3. As an indication that this small folio might be secure. This can
>  	 *    overindicate, e.g. we set the bit before calling
>  	 *    convert_to_secure.
>  	 * As secure pages are never huge, all 3 variants can co-exists.
>  	 */
> -	if (!test_bit(PG_arch_1, &page->flags))
> +	if (!test_bit(PG_arch_1, &folio->flags))
>  		return 0;
>  
> -	rc = uv_pin_shared(page_to_phys(page));
> +	rc = uv_pin_shared(folio_to_phys(folio));
>  	if (!rc) {
> -		clear_bit(PG_arch_1, &page->flags);
> +		clear_bit(PG_arch_1, &folio->flags);
>  		return 0;
>  	}
>  
> -	rc = uv_convert_from_secure(page_to_phys(page));
> +	rc = uv_convert_from_secure(folio_to_phys(folio));
>  	if (!rc) {
> -		clear_bit(PG_arch_1, &page->flags);
> +		clear_bit(PG_arch_1, &folio->flags);
>  		return 0;
>  	}
>