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

David Hildenbrand
2024-04-11T10:38:22Z

On 10.04.24 19:42, Claudio Imbrenda wrote:
> 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...

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