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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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