From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mga11.intel.com (mga11.intel.com [192.55.52.93]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 954CA168 for ; Tue, 11 Jan 2022 19:46:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1641930402; x=1673466402; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=gTc4jBDH9a16Q1xuiD12eIuLKoPR30A3hlnu1JbJSQM=; b=Dm8PJ1/swRZEZyTnJXG3AdhQU4Sm6WR2cQUTU3nl8Z4udlYsnM3oMJlj 2qY77Dtshs+Scpy6+6+HQved4ACTpaZvc+loZv84RzptNxslBcC7Hd2sa 7pnwUyOB7wrudZMpJBZppUe8Hc8umzB6uzv6NPkjEWggwjroCy4hSV1xZ II9P5wAoUFTl/o4QVh5J3EdumzAJXrqqMc3ZDWu3QrZ4HINgUqGhOMCcp nP7CBRxHNSbUkCvKQJnHWToowQbqLKPdKdjZR+WPaWyQMALD2XY/Ug5IJ 8Kv/kh/2Q4lVTIdhNaCRgmbc+DP3wz3fMvjO9G0Cv0Zl2Qp1rJU77Zkg/ A==; X-IronPort-AV: E=McAfee;i="6200,9189,10224"; a="241123202" X-IronPort-AV: E=Sophos;i="5.88,279,1635231600"; d="scan'208";a="241123202" Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 11 Jan 2022 11:46:41 -0800 X-IronPort-AV: E=Sophos;i="5.88,279,1635231600"; d="scan'208";a="613324769" Received: from padhika1-mobl.amr.corp.intel.com (HELO [10.209.13.65]) ([10.209.13.65]) by fmsmga003-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 11 Jan 2022 11:46:40 -0800 Message-ID: <3a68fabd-eaff-2164-5609-3a71fd4a7257@intel.com> Date: Tue, 11 Jan 2022 11:46:37 -0800 Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.4.1 Subject: Re: [PATCHv2 1/7] mm: Add support for unaccepted memory Content-Language: en-US To: "Kirill A. Shutemov" , Borislav Petkov , Andy Lutomirski , Sean Christopherson , Andrew Morton , Joerg Roedel , Ard Biesheuvel Cc: Andi Kleen , Kuppuswamy Sathyanarayanan , David Rientjes , Vlastimil Babka , Tom Lendacky , Thomas Gleixner , Peter Zijlstra , Paolo Bonzini , Ingo Molnar , Varad Gautam , Dario Faggioli , x86@kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev, linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org References: <20220111113314.27173-1-kirill.shutemov@linux.intel.com> <20220111113314.27173-2-kirill.shutemov@linux.intel.com> From: Dave Hansen In-Reply-To: <20220111113314.27173-2-kirill.shutemov@linux.intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit > diff --git a/mm/memblock.c b/mm/memblock.c > index 1018e50566f3..6dfa594192de 100644 > --- a/mm/memblock.c > +++ b/mm/memblock.c > @@ -1400,6 +1400,7 @@ phys_addr_t __init memblock_alloc_range_nid(phys_addr_t size, > */ > kmemleak_alloc_phys(found, size, 0, 0); > > + accept_memory(found, found + size); > return found; > } This could use a comment. Looking at this, I also have to wonder if accept_memory() is a bit too generic. Should it perhaps be: cc_accept_memory() or cc_guest_accept_memory()? > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index c5952749ad40..5707b4b5f774 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1064,6 +1064,7 @@ static inline void __free_one_page(struct page *page, > unsigned int max_order; > struct page *buddy; > bool to_tail; > + bool offline = PageOffline(page); > > max_order = min_t(unsigned int, MAX_ORDER - 1, pageblock_order); > > @@ -1097,6 +1098,10 @@ 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 (PageOffline(buddy)) > + offline = true; > + > combined_pfn = buddy_pfn & pfn; > page = page + (combined_pfn - pfn); > pfn = combined_pfn; > @@ -1130,6 +1135,9 @@ static inline void __free_one_page(struct page *page, > done_merging: > set_buddy_order(page, order); > > + if (offline) > + __SetPageOffline(page); > + > if (fpi_flags & FPI_TO_TAIL) > to_tail = true; > else if (is_shuffle_order(order)) This is touching some pretty hot code paths. You mention both that accepting memory is slow and expensive, yet you're doing it in the core allocator. That needs at least some discussion in the changelog. > @@ -1155,7 +1163,8 @@ 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) && > + !PageOffline(page)) > return false; Looking at stuff like this, I can't help but think that a: #define PageOffline PageUnaccepted and some other renaming would be a fine idea. I get that the Offline bit can be reused, but I'm not sure that the "Offline" *naming* should be reused. What you're doing here is logically distinct from existing offlining. > if (unlikely((unsigned long)page->mapping | > @@ -1734,6 +1743,8 @@ void __init memblock_free_pages(struct page *page, unsigned long pfn, > { > if (early_page_uninitialised(pfn)) > return; > + > + maybe_set_page_offline(page, order); > __free_pages_core(page, order); > } > > @@ -1823,10 +1834,12 @@ static void __init deferred_free_range(unsigned long pfn, > if (nr_pages == pageblock_nr_pages && > (pfn & (pageblock_nr_pages - 1)) == 0) { > set_pageblock_migratetype(page, MIGRATE_MOVABLE); > + maybe_set_page_offline(page, pageblock_order); > __free_pages_core(page, pageblock_order); > 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); > @@ -2297,6 +2310,9 @@ static inline void expand(struct zone *zone, struct page *page, > if (set_page_guard(zone, &page[size], high, migratetype)) > continue; > > + if (PageOffline(page)) > + __SetPageOffline(&page[size]); Yeah, this is really begging for comments. Please add some. > add_to_free_list(&page[size], zone, high, migratetype); > set_buddy_order(&page[size], high); > } > @@ -2393,6 +2409,9 @@ inline void post_alloc_hook(struct page *page, unsigned int order, > */ > kernel_unpoison_pages(page, 1 << order); > > + if (PageOffline(page)) > + accept_and_clear_page_offline(page, order); > + > /* > * As memory initialization might be integrated into KASAN, > * kasan_alloc_pages and kernel_init_free_pages must be I guess once there are no more PageOffline() pages in the allocator, the only impact from these patches will be a bunch of conditional branches from the "if (PageOffline(page))" that always have the same result. The branch predictors should do a good job with that. *BUT*, that overhead is going to be universally inflicted on all users on x86, even those without TDX. I guess the compiler will save non-x86 users because they'll have an empty stub for accept_and_clear_page_offline() which the compiler will optimize away. It sure would be nice to have some changelog material about why this is OK, though. This is especially true since there's a global spinlock hidden in accept_and_clear_page_offline() wrapping a slow and "costly" operation.