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

Claudio Imbrenda
2024-04-10T17:44:58Z

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;
> }
>