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SubjectRe: [PATCHv5 12/19] x86/mm: Implement prep_encrypted_page() and arch_free_page()
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The description doesn't mention the potential performance implications
of this patch. That's criminal at this point.

> --- a/arch/x86/mm/mktme.c
> +++ b/arch/x86/mm/mktme.c
> @@ -1,4 +1,5 @@
> #include <linux/mm.h>
> +#include <linux/highmem.h>
> #include <asm/mktme.h>
>
> phys_addr_t mktme_keyid_mask;
> @@ -49,3 +50,51 @@ int vma_keyid(struct vm_area_struct *vma)
> prot = pgprot_val(vma->vm_page_prot);
> return (prot & mktme_keyid_mask) >> mktme_keyid_shift;
> }
> +
> +void prep_encrypted_page(struct page *page, int order, int keyid, bool zero)
> +{
> + int i;
> +
> + /* It's not encrypted page: nothing to do */
> + if (!keyid)
> + return;

prep_encrypted_page() is called in the fast path in the page allocator.
This out-of-line copy costs a function call for all users and this is
also out of the reach of the compiler to understand that keyid!=0 is
unlikely.

I think this needs to be treated to the inline-in-the-header treatment.

> + /*
> + * The hardware/CPU does not enforce coherency between mappings of the
> + * same physical page with different KeyIDs or encryption keys.
> + * We are responsible for cache management.
> + *
> + * We flush cache before allocating encrypted page
> + */
> + clflush_cache_range(page_address(page), PAGE_SIZE << order);

It's also worth pointing out that this must be done on the keyid alias
direct map, not the normal one.

Wait a sec... How do we know which direct map to use?

> + for (i = 0; i < (1 << order); i++) {
> + /* All pages coming out of the allocator should have KeyID 0 */
> + WARN_ON_ONCE(lookup_page_ext(page)->keyid);
> + lookup_page_ext(page)->keyid = keyid;
> +
> + /* Clear the page after the KeyID is set. */
> + if (zero)
> + clear_highpage(page);
> +
> + page++;
> + }
> +}
> +
> +void arch_free_page(struct page *page, int order)
> +{
> + int i;
> +
> + /* It's not encrypted page: nothing to do */
> + if (!page_keyid(page))
> + return;

Ditto on pushing this to a header.

> + clflush_cache_range(page_address(page), PAGE_SIZE << order);

OK, how do we know which copy of the direct map to use, here?

> + for (i = 0; i < (1 << order); i++) {
> + /* Check if the page has reasonable KeyID */
> + WARN_ON_ONCE(lookup_page_ext(page)->keyid > mktme_nr_keyids);
> + lookup_page_ext(page)->keyid = 0;
> + page++;
> + }
> +}
>

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