From: Andres Lagar-Cavilla <andre...@google.com>
Include a small treatise on the locking rules around page teams.
Signed-off-by: Andres Lagar-Cavilla <andre...@google.com>
Signed-off-by: Hugh Dickins <hu...@google.com>
---
arch/x86/kvm/mmu.c | 155 +++++++++++++++++++++++++++++------
arch/x86/kvm/paging_tmpl.h | 3
2 files changed, 132 insertions(+), 26 deletions(-)
--- thpfs.orig/arch/x86/kvm/mmu.c 2015-02-20 19:35:20.095835839 -0800
+++ thpfs/arch/x86/kvm/mmu.c 2015-02-20 19:35:24.775825138 -0800
@@ -32,6 +32,7 @@
#include <linux/module.h>
#include <linux/swap.h>
#include <linux/hugetlb.h>
+#include <linux/pageteam.h>
#include <linux/compiler.h>
#include <linux/srcu.h>
#include <linux/slab.h>
@@ -2723,7 +2724,106 @@ static int kvm_handle_bad_page(struct kv
return -EFAULT;
}
+/*
+ * We are holding kvm->mmu_lock, serializing against mmu notifiers.
+ * We have a ref on page.
+ *
+ * A team of tmpfs 512 pages can be mapped as an integral hugepage as long as
+ * the team is not disbanded. The head page is !PageTeam if disbanded.
+ *
+ * Huge tmpfs pages are disbanded for page freeing, shrinking, or swap out.
+ *
+ * Freeing (punch hole, truncation):
+ * shmem_undo_range
+ * disband
+ * lock head page
+ * unmap_mapping_range
+ * zap_page_range_single
+ * mmu_notifier_invalidate_range_start
+ * split_huge_page_pmd or zap_huge_pmd
+ * remap_team_by_ptes
+ * mmu_notifier_invalidate_range_end
+ * unlock head page
+ * pagevec_release
+ * pages are freed
+ * If we race with disband MMUN will fix us up. The head page lock also
+ * serializes any gup() against resolving the page team.
+ *
+ * Shrinker, disbands, but once a page team is fully banded up it no longer is
+ * tagged as shrinkable in the radix tree and hence can't be shrunk.
+ * shmem_shrink_hugehole
+ * shmem_choose_hugehole
+ * disband
+ * migrate_pages
+ * try_to_unmap
+ * mmu_notifier_invalidate_page
+ * Double-indemnity: if we race with disband, MMUN will fix us up.
+ *
+ * Swap out:
+ * shrink_page_list
+ * try_to_unmap
+ * unmap_team_by_pmd
+ * mmu_notifier_invalidate_range
+ * pageout
+ * shmem_writepage
+ * disband
+ * free_hot_cold_page_list
+ * pages are freed
+ * If we race with disband, no one will come to fix us up. So, we check for a
+ * pmd mapping, serializing against the MMUN in unmap_team_by_pmd, which will
+ * break the pmd mapping if it runs before us (or invalidate our mapping if ran
+ * after).
+ *
+ * N.B. migration requires further thought all around.
+ */
+static bool is_huge_tmpfs(struct mm_struct *mm, struct page *page,
+ unsigned long address)
+{
+ pgd_t *pgd;
+ pud_t *pud;
+ pmd_t *pmd;
+ struct page *head;
+
+ if (PageAnon(page) || !PageTeam(page))
+ return false;
+ /*
+ * This strictly assumes PMD-level huge-ing.
+ * Which is the only thing KVM can handle here.
+ * N.B. Assume (like everywhere else) PAGE_SIZE == PAGE_CACHE_SIZE.
+ */
+ if (((address & (HPAGE_PMD_SIZE - 1)) >> PAGE_SHIFT) !=
+ (page->index & (HPAGE_PMD_NR-1)))
+ return false;
+ head = team_head(page);
+ if (!PageTeam(head))
+ return false;
+ /*
+ * Attempt at early discard. If the head races into becoming SwapCache,
+ * and thus having a bogus team_usage, we'll know for sure next.
+ */
+ if (!team_hugely_mapped(head))
+ return false;
+ /*
+ * Open code page_check_address_pmd, otherwise we'd have to make it
+ * a module-visible symbol. Simplify it. No need for page table lock,
+ * as mmu notifier serialization ensures we are on either side of
+ * unmap_team_by_pmd or remap_team_by_ptes.
+ */
+ address &= HPAGE_PMD_MASK;
+ pgd = pgd_offset(mm, address);
+ if (!pgd_present(*pgd))
+ return false;
+ pud = pud_offset(pgd, address);
+ if (!pud_present(*pud))
+ return false;
+ pmd = pmd_offset(pud, address);
+ if (!pmd_trans_huge(*pmd))
+ return false;
+ return pmd_page(*pmd) == head;
+}
+
static void transparent_hugepage_adjust(struct kvm_vcpu *vcpu,
+ unsigned long address,
gfn_t *gfnp, pfn_t *pfnp, int *levelp)
{
pfn_t pfn = *pfnp;
@@ -2737,29 +2837,34 @@ static void transparent_hugepage_adjust(
* here.
*/
if (!is_error_noslot_pfn(pfn) && !kvm_is_reserved_pfn(pfn) &&
- level == PT_PAGE_TABLE_LEVEL &&
- PageTransCompound(pfn_to_page(pfn)) &&
- !has_wrprotected_page(vcpu->kvm, gfn, PT_DIRECTORY_LEVEL)) {
- unsigned long mask;
- /*
- * mmu_notifier_retry was successful and we hold the
- * mmu_lock here, so the pmd can't become splitting
- * from under us, and in turn
- * __split_huge_page_refcount() can't run from under
- * us and we can safely transfer the refcount from
- * PG_tail to PG_head as we switch the pfn to tail to
- * head.
- */
- *levelp = level = PT_DIRECTORY_LEVEL;
- mask = KVM_PAGES_PER_HPAGE(level) - 1;
- VM_BUG_ON((gfn & mask) != (pfn & mask));
- if (pfn & mask) {
- gfn &= ~mask;
- *gfnp = gfn;
- kvm_release_pfn_clean(pfn);
- pfn &= ~mask;
- kvm_get_pfn(pfn);
- *pfnp = pfn;
+ level == PT_PAGE_TABLE_LEVEL) {
+ struct page *page = pfn_to_page(pfn);
+
+ if ((PageTransCompound(page) ||
+ is_huge_tmpfs(vcpu->kvm->mm, page, address)) &&
+ !has_wrprotected_page(vcpu->kvm, gfn,
+ PT_DIRECTORY_LEVEL)) {
+ unsigned long mask;
+ /*
+ * mmu_notifier_retry was successful and we hold the
+ * mmu_lock here, so the pmd can't become splitting
+ * from under us, and in turn
+ * __split_huge_page_refcount() can't run from under
+ * us and we can safely transfer the refcount from
+ * PG_tail to PG_head as we switch the pfn to tail to
+ * head.
+ */
+ *levelp = level = PT_DIRECTORY_LEVEL;
+ mask = KVM_PAGES_PER_HPAGE(level) - 1;
+ VM_BUG_ON((gfn & mask) != (pfn & mask));
+ if (pfn & mask) {
+ gfn &= ~mask;
+ *gfnp = gfn;
+ kvm_release_pfn_clean(pfn);
+ pfn &= ~mask;
+ kvm_get_pfn(pfn);
+ *pfnp = pfn;
+ }
}
}
}
@@ -2955,7 +3060,7 @@ static int nonpaging_map(struct kvm_vcpu
goto out_unlock;
make_mmu_pages_available(vcpu);
if (likely(!force_pt_level))
- transparent_hugepage_adjust(vcpu, &gfn, &pfn, &level);
+ transparent_hugepage_adjust(vcpu, hva, &gfn, &pfn, &level);
r = __direct_map(vcpu, v, write, map_writable, level, gfn, pfn,
prefault);
spin_unlock(&vcpu->kvm->mmu_lock);
@@ -3440,7 +3545,7 @@ static int tdp_page_fault(struct kvm_vcp
goto out_unlock;
make_mmu_pages_available(vcpu);
if (likely(!force_pt_level))
- transparent_hugepage_adjust(vcpu, &gfn, &pfn, &level);
+ transparent_hugepage_adjust(vcpu, hva, &gfn, &pfn, &level);
r = __direct_map(vcpu, gpa, write, map_writable,
level, gfn, pfn, prefault);
spin_unlock(&vcpu->kvm->mmu_lock);
--- thpfs.orig/arch/x86/kvm/paging_tmpl.h 2015-02-20 19:35:20.095835839
-0800
+++ thpfs/arch/x86/kvm/paging_tmpl.h 2015-02-20 19:35:24.775825138 -0800
@@ -794,7 +794,8 @@ static int FNAME(page_fault)(struct kvm_
kvm_mmu_audit(vcpu, AUDIT_PRE_PAGE_FAULT);
make_mmu_pages_available(vcpu);
if (!force_pt_level)
- transparent_hugepage_adjust(vcpu, &walker.gfn, &pfn, &level);
+ transparent_hugepage_adjust(vcpu, hva, &walker.gfn, &pfn,
+ &level);
r = FNAME(fetch)(vcpu, addr, &walker, write_fault,
level, pfn, map_writable, prefault);
++vcpu->stat.pf_fixed;
--
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