From: Dave Hansen <dave.hansen@intel.com>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>,
Sean Christopherson <seanjc@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Joerg Roedel <jroedel@suse.de>, Ard Biesheuvel <ardb@kernel.org>
Cc: Andi Kleen <ak@linux.intel.com>,
Kuppuswamy Sathyanarayanan
<sathyanarayanan.kuppuswamy@linux.intel.com>,
David Rientjes <rientjes@google.com>,
Vlastimil Babka <vbabka@suse.cz>,
Tom Lendacky <thomas.lendacky@amd.com>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
Paolo Bonzini <pbonzini@redhat.com>,
Ingo Molnar <mingo@redhat.com>,
Varad Gautam <varad.gautam@suse.com>,
Dario Faggioli <dfaggioli@suse.com>,
Brijesh Singh <brijesh.singh@amd.com>,
Mike Rapoport <rppt@kernel.org>,
David Hildenbrand <david@redhat.com>,
x86@kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev,
linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org,
Mike Rapoport <rppt@linux.ibm.com>
Subject: Re: [PATCHv4 1/8] mm: Add support for unaccepted memory
Date: Fri, 8 Apr 2022 11:55:43 -0700 [thread overview]
Message-ID: <767c2100-c171-1fd3-6a92-0af2e4bf3067@intel.com> (raw)
In-Reply-To: <20220405234343.74045-2-kirill.shutemov@linux.intel.com>
On 4/5/22 16:43, 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
^ require
> guest. Accepting happens via a protocol specific for the Virtual Machine
> platform.
^ s/for/to
> 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.
> PageUnaccepted() is used to indicate that the page requires acceptance.
Does this consume an actual page flag or is it aliased?
> Kernel only needs 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
> PageUnaccepted() in allocate and free paths. The check refers a hot
^ to
...
> + /*
> + * PageUnaccepted() 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.
> + */
Let's talk about "used" with a bit more detail. Maybe:
/*
* PageUnaccepted() indicates that the page has to be "accepted" before
* it can be read or written. The page allocator must to call
* accept_page() before touching the page or returning it to the caller.
*/
...
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 2db95780e003..53f4aa1c92a7 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -121,6 +121,12 @@ typedef int __bitwise fpi_t;
> */
> #define FPI_SKIP_KASAN_POISON ((__force fpi_t)BIT(2))
>
> +/*
> + * Check if the page needs to be marked as PageUnaccepted().
> + * Used for the new pages added to the buddy allocator for the first time.
> + */
> +#define FPI_UNACCEPTED ((__force fpi_t)BIT(3))
> +
> /* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */
> static DEFINE_MUTEX(pcp_batch_high_lock);
> #define MIN_PERCPU_PAGELIST_HIGH_FRACTION (8)
> @@ -1023,6 +1029,26 @@ buddy_merge_likely(unsigned long pfn, unsigned long buddy_pfn,
> return page_is_buddy(higher_page, higher_buddy, order + 1);
> }
>
> +static void accept_page(struct page *page, unsigned int order)
> +{
> + phys_addr_t start = page_to_phys(page);
> + int i;
> +
> + accept_memory(start, start + (PAGE_SIZE << order));
> +
> + for (i = 0; i < (1 << order); i++) {
> + if (PageUnaccepted(page + i))
> + __ClearPageUnaccepted(page + i);
> + }
> +}
It's probably worth a comment somewhere that this can be really slow.
> +static bool page_is_unaccepted(struct page *page, unsigned int order)
> +{
> + phys_addr_t start = page_to_phys(page);
> +
> + return memory_is_unaccepted(start, start + (PAGE_SIZE << order));
> +}
> +
> /*
> * Freeing function for a buddy system allocator.
> *
> @@ -1058,6 +1084,7 @@ static inline void __free_one_page(struct page *page,
> unsigned long combined_pfn;
> struct page *buddy;
> bool to_tail;
> + bool unaccepted = PageUnaccepted(page);
>
> VM_BUG_ON(!zone_is_initialized(zone));
> VM_BUG_ON_PAGE(page->flags & PAGE_FLAGS_CHECK_AT_PREP, page);
> @@ -1089,6 +1116,11 @@ 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);
> +
> + /* Mark page unaccepted if any of merged pages were unaccepted */
> + if (PageUnaccepted(buddy))
> + unaccepted = true;
Naming nit: following the logic with a double-negative like !unaccepted
is a bit hard. Would this be more readable if it were:
bool page_needs_acceptance = PageUnaccepted(page);
and then the code below...
> combined_pfn = buddy_pfn & pfn;
> page = page + (combined_pfn - pfn);
> pfn = combined_pfn;
> @@ -1124,6 +1156,17 @@ static inline void __free_one_page(struct page *page,
> done_merging:
> set_buddy_order(page, order);
>
> + /*
> + * Check if the page needs to be marked as PageUnaccepted().
> + * Used for the new pages added to the buddy allocator for the first
> + * time.
> + */
> + if (!unaccepted && (fpi_flags & FPI_UNACCEPTED))
> + unaccepted = page_is_unaccepted(page, order);
if (page_needs_acceptance && (fpi_flags & FPI_UNACCEPTED))
page_needs_acceptance = page_is_unaccepted(page, order);
> + if (unaccepted)
> + __SetPageUnaccepted(page);
This is getting hard for me to follow.
There are:
1. Pages that come in here with PageUnaccepted()==1
2. Pages that come in here with PageUnaccepted()==0, but a buddy that
was PageUnaccepted()==1
In either of those cases, the bitmap will be consulted to see if the
page is *truly* unaccepted or not. But, I'm struggling to figure out
how a page could end up in one of those scenarios and *not* be
page_is_unaccepted().
There are three pieces of information that come in:
1. PageUnaccepted(page)
2. PageUnaccepted(buddies[])
3. the bitmap
and one piece of information going out:
PageUnaccepted(page);
I think I need a more coherent description of how those four things fit
together.
> if (fpi_flags & FPI_TO_TAIL)
> to_tail = true;
> else if (is_shuffle_order(order))
> @@ -1149,7 +1192,8 @@ 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) &&
> + !PageUnaccepted(page))
> return false;
That probably deserves a comment, and maybe its own if() statement.
> if (unlikely((unsigned long)page->mapping |
> @@ -1654,7 +1698,8 @@ void __free_pages_core(struct page *page, unsigned int order)
> * Bypass PCP and place fresh pages right to the tail, primarily
> * relevant for memory onlining.
> */
> - __free_pages_ok(page, order, FPI_TO_TAIL | FPI_SKIP_KASAN_POISON);
> + __free_pages_ok(page, order,
> + FPI_TO_TAIL | FPI_SKIP_KASAN_POISON | FPI_UNACCEPTED);
> }
>
> #ifdef CONFIG_NUMA
> @@ -1807,6 +1852,7 @@ static void __init deferred_free_range(unsigned long pfn,
> return;
> }
>
> + accept_memory(pfn << PAGE_SHIFT, (pfn + nr_pages) << PAGE_SHIFT);
> for (i = 0; i < nr_pages; i++, page++, pfn++) {
> if ((pfn & (pageblock_nr_pages - 1)) == 0)
> set_pageblock_migratetype(page, MIGRATE_MOVABLE);
Comment, please. I assume doing the slow accept up front is OK here
because this is in the deferred path. But, it would be nice to know for
sure.
> @@ -2266,6 +2312,10 @@ static inline void expand(struct zone *zone, struct page *page,
> if (set_page_guard(zone, &page[size], high, migratetype))
> continue;
>
> + /* Transfer PageUnaccepted() to the newly split pages */
> + if (PageUnaccepted(page))
> + __SetPageUnaccepted(&page[size]);
We don't want to just accept the page here, right? Because we're
holding the zone lock? Maybe we should mention that:
/*
* Transfer PageUnaccepted() to the newly split pages so
* they can be accepted after dropping the zone lock.
*/
> add_to_free_list(&page[size], zone, high, migratetype);
> set_buddy_order(&page[size], high);
> }
> @@ -2396,6 +2446,9 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
> */
> kernel_unpoison_pages(page, 1 << order);
>
> + if (PageUnaccepted(page))
> + accept_page(page, order);
> +
> /*
> * As memory initialization might be integrated into KASAN,
> * KASAN unpoisoning and memory initializion code must be
Is accepted memory guaranteed to be zeroed? Do we want to skip the
__GFP_ZERO behavior later in this function? Or is that just a silly
over-optimization?
next prev parent reply other threads:[~2022-04-08 18:56 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-05 23:43 [PATCHv4 0/8] mm, x86/cc: Implement support for unaccepted memory Kirill A. Shutemov
2022-04-05 23:43 ` [PATCHv4 1/8] mm: Add " Kirill A. Shutemov
2022-04-08 18:55 ` Dave Hansen [this message]
2022-04-09 15:54 ` Kirill A. Shutemov
2022-04-11 6:38 ` Dave Hansen
2022-04-11 10:07 ` Mike Rapoport
2022-04-13 11:40 ` Kirill A. Shutemov
2022-04-13 14:48 ` Mike Rapoport
2022-04-13 15:15 ` Kirill A. Shutemov
2022-04-13 20:06 ` Mike Rapoport
2022-04-11 8:47 ` David Hildenbrand
2022-04-08 19:04 ` David Hildenbrand
2022-04-08 19:11 ` Dave Hansen
2022-04-09 17:52 ` Kirill A. Shutemov
2022-04-11 6:41 ` Dave Hansen
2022-04-11 15:55 ` Borislav Petkov
2022-04-11 16:27 ` Dave Hansen
2022-04-11 18:55 ` Tom Lendacky
2022-04-12 8:15 ` David Hildenbrand
2022-04-12 16:08 ` Dave Hansen
2022-04-13 10:36 ` David Hildenbrand
2022-04-13 11:30 ` Kirill A. Shutemov
2022-04-13 11:32 ` David Hildenbrand
2022-04-13 15:36 ` Dave Hansen
2022-04-13 16:07 ` David Hildenbrand
2022-04-13 16:13 ` Dave Hansen
2022-04-13 16:24 ` Kirill A. Shutemov
2022-04-13 14:39 ` Mike Rapoport
2022-04-05 23:43 ` [PATCHv4 2/8] efi/x86: Get full memory map in allocate_e820() Kirill A. Shutemov
[not found] ` <Ylae+bejPzRMPrDw@zn.tnic>
2022-04-13 11:45 ` Kirill A. Shutemov
2022-04-05 23:43 ` [PATCHv4 3/8] efi/x86: Implement support for unaccepted memory Kirill A. Shutemov
2022-04-08 17:26 ` Dave Hansen
2022-04-09 19:41 ` Kirill A. Shutemov
2022-04-14 15:55 ` Borislav Petkov
2022-04-15 22:24 ` Borislav Petkov
2022-04-18 15:55 ` Kirill A. Shutemov
2022-04-18 16:38 ` Borislav Petkov
2022-04-18 20:24 ` Kirill A. Shutemov
2022-04-18 21:01 ` Borislav Petkov
2022-04-18 23:50 ` Kirill A. Shutemov
2022-04-19 7:39 ` Borislav Petkov
2022-04-19 15:30 ` Kirill A. Shutemov
2022-04-19 16:38 ` Dave Hansen
2022-04-19 19:23 ` Borislav Petkov
2022-04-21 12:26 ` Borislav Petkov
2022-04-22 0:21 ` Kirill A. Shutemov
2022-04-22 9:30 ` Borislav Petkov
2022-04-22 13:26 ` Kirill A. Shutemov
2022-04-05 23:43 ` [PATCHv4 4/8] x86/boot/compressed: Handle " Kirill A. Shutemov
2022-04-08 17:57 ` Dave Hansen
2022-04-09 20:20 ` Kirill A. Shutemov
2022-04-11 6:49 ` Dave Hansen
2022-04-05 23:43 ` [PATCHv4 5/8] x86/mm: Reserve unaccepted memory bitmap Kirill A. Shutemov
2022-04-08 18:08 ` Dave Hansen
2022-04-09 20:43 ` Kirill A. Shutemov
2022-04-05 23:43 ` [PATCHv4 6/8] x86/mm: Provide helpers for unaccepted memory Kirill A. Shutemov
2022-04-08 18:15 ` Dave Hansen
2022-04-08 19:21 ` Dave Hansen
2022-04-13 16:08 ` Kirill A. Shutemov
2022-04-05 23:43 ` [PATCHv4 7/8] x86/tdx: Unaccepted memory support Kirill A. Shutemov
2022-04-08 18:28 ` Dave Hansen
2022-04-05 23:43 ` [PATCHv4 8/8] mm/vmstat: Add counter for memory accepting Kirill A. Shutemov
2022-04-12 8:18 ` David Hildenbrand
2022-04-08 17:02 ` [PATCHv4 0/8] mm, x86/cc: Implement support for unaccepted memory Dave Hansen
2022-04-09 23:44 ` Kirill A. Shutemov
2022-04-21 12:29 ` Borislav Petkov
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