Re: [PATCH v1 3/5] s390/uv: convert PG_arch_1 users to only work on small folios

[David Hildenbrand]

On 10.04.24 19:42, Claudio Imbrenda wrote:
> On Thu,  4 Apr 2024 18:36:40 +0200
> David Hildenbrand <david@xxxxxxxxxx> 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@xxxxxxxxxx>
> > ---
> >   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...


Will use

"/* See gmap_make_secure(): large folios cannot be protected */"

> > +
> > +	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

here as well and ...

> > +
> > +	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 */

^ here as well.

> > +	if (unlikely(folio_test_large(folio)))
> >   		return 0;
> >   

--
Cheers,

David / dhildenb