On 31.01.22 13:13, David Hildenbrand wrote:
> On 30.01.22 17:45, Kirill A. Shutemov wrote:
>> UEFI Specification version 2.9 introduces the concept of memory
>> acceptance. Some Virtual Machine platforms, such as Intel TDX or AMD
>> SEV-SNP, requiring memory to be accepted before it can be used by the
>> guest. Accepting happens via a protocol specific for the Virtual Machine
>> platform.
>>
>> Accepting memory is costly and it makes VMM allocate memory for the
>> accepted guest physical address range. It's better to postpone memory
>> acceptance until memory is needed. It lowers boot time and reduces
>> memory overhead.
>>
>> Support of such memory requires a few changes in core-mm code:
>>
>> - memblock has to accept memory on allocation;
>>
>> - page allocator has to accept memory on the first allocation of the
>> page;
>>
>> Memblock change is trivial.
>>
>> The page allocator is modified to accept pages on the first allocation.
>> PageBuddyUnaccepted() is used to indicate that the page requires acceptance.
>>
>> Kernel only need to accept memory once after boot, so during the boot
>> and warm up phase there will be a lot of memory acceptance. After things
>> are settled down the only price of the feature if couple of checks for
>> PageBuddyUnaccepted() in alloc and free paths. The check refers a hot
>> variable (that also encodes PageBuddy()), so it is cheap and not visible
>> on profiles.
>>
>> Architecture has to provide three helpers if it wants to support
>> unaccepted memory:
>>
>> - accept_memory() makes a range of physical addresses accepted.
>>
>> - maybe_mark_page_unaccepted() marks a page PageBuddyUnaccepted() if it
>> requires acceptance. Used during boot to put pages on free lists.
>>
>> - accept_page() makes a page accepted and clears PageBuddyUnaccepted().
>>
>> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
>> Acked-by: Mike Rapoport <rppt@xxxxxxxxxxxxx> # memblock
>
>
> You should somehow document+check+enforce that page poisoning cannot be
> enabled concurrently, because it cannot possibly work IIUC.
>
> [...]
>
>> + /*
>> + * PageBuddyUnaccepted() indicates that the page has to be "accepted" before
>> + * it can be used. Page allocator has to call accept_page() before returning
>> + * the page to the caller.
>> + *
>> + * PageBuddyUnaccepted() encoded with the same bit as PageOffline().
>> + * PageOffline() pages are never on free list of buddy allocator, so there's
>> + * not conflict.
>> + */
>> +#ifdef CONFIG_UNACCEPTED_MEMORY
>> +PAGE_TYPE_OPS(BuddyUnaccepted, offline)
>> +#else
>> +PAGE_TYPE_OPS_FALSE(BuddyUnaccepted)
>> +#endif
>
> Much better.
>
>> +
>> extern void page_offline_freeze(void);
>> extern void page_offline_thaw(void);
>> extern void page_offline_begin(void);
>> diff --git a/mm/internal.h b/mm/internal.h
>> index d80300392a19..26e5d7cb6aff 100644
>> --- a/mm/internal.h
>> +++ b/mm/internal.h
>> @@ -718,4 +718,19 @@ void vunmap_range_noflush(unsigned long start, unsigned long end);
>> int numa_migrate_prep(struct page *page, struct vm_area_struct *vma,
>> unsigned long addr, int page_nid, int *flags);
>>
>> +#ifndef CONFIG_UNACCEPTED_MEMORY
>> +static inline void maybe_mark_page_unaccepted(struct page *page,
>> + unsigned int order)
>> +{
>> +}
>> +
>> +static inline void accept_page(struct page *page, unsigned int order)
>> +{
>> +}
>> +
>> +static inline void accept_memory(phys_addr_t start, phys_addr_t end)
>> +{
>> +}
>> +#endif
>> +
>> #endif /* __MM_INTERNAL_H */
>> diff --git a/mm/memblock.c b/mm/memblock.c
>> index 1018e50566f3..6c109b3b2a02 100644
>> --- a/mm/memblock.c
>> +++ b/mm/memblock.c
>> @@ -1400,6 +1400,15 @@ phys_addr_t __init memblock_alloc_range_nid(phys_addr_t size,
>> */
>> kmemleak_alloc_phys(found, size, 0, 0);
>>
>> + /*
>> + * Some Virtual Machine platforms, such as Intel TDX or AMD SEV-SNP,
>> + * require memory to be accepted before it can be used by the
>> + * guest.
>> + *
>> + * Accept the memory of the allocated buffer.
>> + */
>> + accept_memory(found, found + size);
>> +
>> return found;
>> }
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 3589febc6d31..27b9bd20e675 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -1077,6 +1077,7 @@ static inline void __free_one_page(struct page *page,
>> unsigned int max_order;
>> struct page *buddy;
>> bool to_tail;
>> + bool unaccepted = PageBuddyUnaccepted(page);
>>
>> max_order = min_t(unsigned int, MAX_ORDER - 1, pageblock_order);
>>
>> @@ -1110,6 +1111,10 @@ static inline void __free_one_page(struct page *page,
>> clear_page_guard(zone, buddy, order, migratetype);
>> else
>> del_page_from_free_list(buddy, zone, order);
>> +
>> + if (PageBuddyUnaccepted(buddy))
>> + unaccepted = true;
>> +
>> combined_pfn = buddy_pfn & pfn;
>> page = page + (combined_pfn - pfn);
>> pfn = combined_pfn;
>> @@ -1143,6 +1148,10 @@ static inline void __free_one_page(struct page *page,
>> done_merging:
>> set_buddy_order(page, order);
>>
>> + /* Mark page unaccepted if any of merged pages were unaccepted */
>> + if (unaccepted)
>> + __SetPageBuddyUnaccepted(page);
>> +
>> if (fpi_flags & FPI_TO_TAIL)
>> to_tail = true;
>> else if (is_shuffle_order(order))
>> @@ -1168,7 +1177,8 @@ static inline void __free_one_page(struct page *page,
>> static inline bool page_expected_state(struct page *page,
>> unsigned long check_flags)
>> {
>> - if (unlikely(atomic_read(&page->_mapcount) != -1))
>> + if (unlikely(atomic_read(&page->_mapcount) != -1) &&
>> + !PageBuddyUnaccepted(page))
>> return false;
>>
>> if (unlikely((unsigned long)page->mapping |
>> @@ -1749,6 +1759,8 @@ void __init memblock_free_pages(struct page *page, unsigned long pfn,
>> {
>> if (early_page_uninitialised(pfn))
>> return;
>> +
>> + maybe_mark_page_unaccepted(page, order);
>> __free_pages_core(page, order);
>
> You'll be setting the page as unaccepted even before it's actually
> PageBuddy(). While that works, I wonder why we call
> maybe_mark_page_unaccepted() at these points.
>
> Why are we not moving that deeper into the buddy? __free_pages_core() is
> used for any fresh pages that enter the buddy, used outside of
> page_alloc.c only for memory hot(un)plug, so I'd suggest moving it at
> least into there.
>
> But maybe we'd even move it further down, to the place where we actually
> establish PageBuddy().
>
> One idea would be adding a new FPI_UNACCEPTED flag, passing it from
> __free_pages_core() only, and calling maybe_mark_page_unaccepted() from
> __free_one_page() after set_buddy_order().
>
> If in-lining would do its job properly, we'd be left with the
> FPI_UNACCEPTED checks only when called via __free_pages_core(), and we'd
> have that call at a single place right where we mess with PageBuddy().
>
Whops, I forgot
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Because the general approach LGTM.
--
Thanks,
David / dhildenb
