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-rw-r--r--system/xen/xsa/xsa299-4.12-0003-x86-mm-Separate-out-partial_pte-tristate-into-indivi.patch618
1 files changed, 618 insertions, 0 deletions
diff --git a/system/xen/xsa/xsa299-4.12-0003-x86-mm-Separate-out-partial_pte-tristate-into-indivi.patch b/system/xen/xsa/xsa299-4.12-0003-x86-mm-Separate-out-partial_pte-tristate-into-indivi.patch
new file mode 100644
index 0000000000..226e5487b1
--- /dev/null
+++ b/system/xen/xsa/xsa299-4.12-0003-x86-mm-Separate-out-partial_pte-tristate-into-indivi.patch
@@ -0,0 +1,618 @@
+From 0f9f61e5737fdd346550ec6e30161fa99e4653fa Mon Sep 17 00:00:00 2001
+From: George Dunlap <george.dunlap@citrix.com>
+Date: Thu, 10 Oct 2019 17:57:49 +0100
+Subject: [PATCH 03/11] x86/mm: Separate out partial_pte tristate into
+ individual flags
+
+At the moment, partial_pte is a tri-state that contains two distinct bits
+of information:
+
+1. If zero, the pte at index [nr_validated_ptes] is un-validated. If
+ non-zero, the pte was last seen with PGT_partial set.
+
+2. If positive, the pte at index [nr_validated_ptes] does not hold a
+ general reference count. If negative, it does.
+
+To make future patches more clear, separate out this functionality
+into two distinct, named bits: PTF_partial_set (for #1) and
+PTF_partial_general_ref (for #2).
+
+Additionally, a number of functions which need this information also
+take other flags to control behavior (such as `preemptible` and
+`defer`). These are hard to read in the caller (since you only see
+'true' or 'false'), and ugly when many are added together. In
+preparation for adding yet another flag in a future patch, collapse
+all of these into a single `flag` variable.
+
+NB that this does mean checking for what was previously the '-1'
+condition a bit more ugly in the put_page_from_lNe functions (since
+you have to check for both partial_set and general ref); but this
+clause will go away in a future patch.
+
+Also note that the original comment had an off-by-one error:
+partial_flags (like partial_pte before it) concerns
+plNe[nr_validated_ptes], not plNe[nr_validated_ptes+1].
+
+No functional change intended.
+
+This is part of XSA-299.
+
+Reported-by: George Dunlap <george.dunlap@citrix.com>
+Signed-off-by: George Dunlap <george.dunlap@citrix.com>
+Reviewed-by: Jan Beulich <jbeulich@suse.com>
+---
+ xen/arch/x86/mm.c | 165 ++++++++++++++++++++++++---------------
+ xen/include/asm-x86/mm.h | 41 +++++++---
+ 2 files changed, 128 insertions(+), 78 deletions(-)
+
+diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
+index a1b55c10ff..3f6f8cc9b8 100644
+--- a/xen/arch/x86/mm.c
++++ b/xen/arch/x86/mm.c
+@@ -1094,20 +1094,35 @@ get_page_from_l1e(
+ }
+
+ #ifdef CONFIG_PV
++
++/*
++ * The following flags are used to specify behavior of various get and
++ * put commands. The first two are also stored in page->partial_flags
++ * to indicate the state of the page pointed to by
++ * page->pte[page->nr_validated_entries]. See the comment in mm.h for
++ * more information.
++ */
++#define PTF_partial_set (1 << 0)
++#define PTF_partial_general_ref (1 << 1)
++#define PTF_preemptible (1 << 2)
++#define PTF_defer (1 << 3)
++
+ static int get_page_and_type_from_mfn(
+ mfn_t mfn, unsigned long type, struct domain *d,
+- int partial, int preemptible)
++ unsigned int flags)
+ {
+ struct page_info *page = mfn_to_page(mfn);
+ int rc;
++ bool preemptible = flags & PTF_preemptible,
++ partial_ref = flags & PTF_partial_general_ref;
+
+- if ( likely(partial >= 0) &&
++ if ( likely(!partial_ref) &&
+ unlikely(!get_page_from_mfn(mfn, d)) )
+ return -EINVAL;
+
+ rc = _get_page_type(page, type, preemptible);
+
+- if ( unlikely(rc) && partial >= 0 &&
++ if ( unlikely(rc) && !partial_ref &&
+ (!preemptible || page != current->arch.old_guest_table) )
+ put_page(page);
+
+@@ -1117,7 +1132,7 @@ static int get_page_and_type_from_mfn(
+ define_get_linear_pagetable(l2);
+ static int
+ get_page_from_l2e(
+- l2_pgentry_t l2e, unsigned long pfn, struct domain *d, int partial)
++ l2_pgentry_t l2e, unsigned long pfn, struct domain *d, unsigned int flags)
+ {
+ unsigned long mfn = l2e_get_pfn(l2e);
+ int rc;
+@@ -1129,8 +1144,9 @@ get_page_from_l2e(
+ return -EINVAL;
+ }
+
+- rc = get_page_and_type_from_mfn(_mfn(mfn), PGT_l1_page_table, d,
+- partial, false);
++ ASSERT(!(flags & PTF_preemptible));
++
++ rc = get_page_and_type_from_mfn(_mfn(mfn), PGT_l1_page_table, d, flags);
+ if ( unlikely(rc == -EINVAL) && get_l2_linear_pagetable(l2e, pfn, d) )
+ rc = 0;
+
+@@ -1140,7 +1156,7 @@ get_page_from_l2e(
+ define_get_linear_pagetable(l3);
+ static int
+ get_page_from_l3e(
+- l3_pgentry_t l3e, unsigned long pfn, struct domain *d, int partial)
++ l3_pgentry_t l3e, unsigned long pfn, struct domain *d, unsigned int flags)
+ {
+ int rc;
+
+@@ -1152,7 +1168,7 @@ get_page_from_l3e(
+ }
+
+ rc = get_page_and_type_from_mfn(
+- l3e_get_mfn(l3e), PGT_l2_page_table, d, partial, 1);
++ l3e_get_mfn(l3e), PGT_l2_page_table, d, flags | PTF_preemptible);
+ if ( unlikely(rc == -EINVAL) &&
+ !is_pv_32bit_domain(d) &&
+ get_l3_linear_pagetable(l3e, pfn, d) )
+@@ -1164,7 +1180,7 @@ get_page_from_l3e(
+ define_get_linear_pagetable(l4);
+ static int
+ get_page_from_l4e(
+- l4_pgentry_t l4e, unsigned long pfn, struct domain *d, int partial)
++ l4_pgentry_t l4e, unsigned long pfn, struct domain *d, unsigned int flags)
+ {
+ int rc;
+
+@@ -1176,7 +1192,7 @@ get_page_from_l4e(
+ }
+
+ rc = get_page_and_type_from_mfn(
+- l4e_get_mfn(l4e), PGT_l3_page_table, d, partial, 1);
++ l4e_get_mfn(l4e), PGT_l3_page_table, d, flags | PTF_preemptible);
+ if ( unlikely(rc == -EINVAL) && get_l4_linear_pagetable(l4e, pfn, d) )
+ rc = 0;
+
+@@ -1277,7 +1293,7 @@ static void put_data_page(struct page_info *page, bool writeable)
+ * Note also that this automatically deals correctly with linear p.t.'s.
+ */
+ static int put_page_from_l2e(l2_pgentry_t l2e, unsigned long pfn,
+- int partial, bool defer)
++ unsigned int flags)
+ {
+ int rc = 0;
+
+@@ -1300,12 +1316,13 @@ static int put_page_from_l2e(l2_pgentry_t l2e, unsigned long pfn,
+ struct page_info *pg = l2e_get_page(l2e);
+ struct page_info *ptpg = mfn_to_page(_mfn(pfn));
+
+- if ( unlikely(partial > 0) )
++ if ( (flags & (PTF_partial_set | PTF_partial_general_ref)) ==
++ PTF_partial_set )
+ {
+- ASSERT(!defer);
++ ASSERT(!(flags & PTF_defer));
+ rc = _put_page_type(pg, true, ptpg);
+ }
+- else if ( defer )
++ else if ( flags & PTF_defer )
+ {
+ current->arch.old_guest_ptpg = ptpg;
+ current->arch.old_guest_table = pg;
+@@ -1322,7 +1339,7 @@ static int put_page_from_l2e(l2_pgentry_t l2e, unsigned long pfn,
+ }
+
+ static int put_page_from_l3e(l3_pgentry_t l3e, unsigned long pfn,
+- int partial, bool defer)
++ unsigned int flags)
+ {
+ struct page_info *pg;
+ int rc;
+@@ -1345,13 +1362,14 @@ static int put_page_from_l3e(l3_pgentry_t l3e, unsigned long pfn,
+
+ pg = l3e_get_page(l3e);
+
+- if ( unlikely(partial > 0) )
++ if ( (flags & (PTF_partial_set | PTF_partial_general_ref)) ==
++ PTF_partial_set )
+ {
+- ASSERT(!defer);
++ ASSERT(!(flags & PTF_defer));
+ return _put_page_type(pg, true, mfn_to_page(_mfn(pfn)));
+ }
+
+- if ( defer )
++ if ( flags & PTF_defer )
+ {
+ current->arch.old_guest_ptpg = mfn_to_page(_mfn(pfn));
+ current->arch.old_guest_table = pg;
+@@ -1366,7 +1384,7 @@ static int put_page_from_l3e(l3_pgentry_t l3e, unsigned long pfn,
+ }
+
+ static int put_page_from_l4e(l4_pgentry_t l4e, unsigned long pfn,
+- int partial, bool defer)
++ unsigned int flags)
+ {
+ int rc = 1;
+
+@@ -1375,13 +1393,14 @@ static int put_page_from_l4e(l4_pgentry_t l4e, unsigned long pfn,
+ {
+ struct page_info *pg = l4e_get_page(l4e);
+
+- if ( unlikely(partial > 0) )
++ if ( (flags & (PTF_partial_set | PTF_partial_general_ref)) ==
++ PTF_partial_set )
+ {
+- ASSERT(!defer);
++ ASSERT(!(flags & PTF_defer));
+ return _put_page_type(pg, true, mfn_to_page(_mfn(pfn)));
+ }
+
+- if ( defer )
++ if ( flags & PTF_defer )
+ {
+ current->arch.old_guest_ptpg = mfn_to_page(_mfn(pfn));
+ current->arch.old_guest_table = pg;
+@@ -1492,12 +1511,13 @@ static int alloc_l2_table(struct page_info *page, unsigned long type)
+ unsigned long pfn = mfn_x(page_to_mfn(page));
+ l2_pgentry_t *pl2e;
+ unsigned int i;
+- int rc = 0, partial = page->partial_pte;
++ int rc = 0;
++ unsigned int partial_flags = page->partial_flags;
+
+ pl2e = map_domain_page(_mfn(pfn));
+
+ for ( i = page->nr_validated_ptes; i < L2_PAGETABLE_ENTRIES;
+- i++, partial = 0 )
++ i++, partial_flags = 0 )
+ {
+ l2_pgentry_t l2e;
+
+@@ -1520,17 +1540,18 @@ static int alloc_l2_table(struct page_info *page, unsigned long type)
+ rc = -EINTR;
+ }
+ else
+- rc = get_page_from_l2e(l2e, pfn, d, partial);
++ rc = get_page_from_l2e(l2e, pfn, d, partial_flags);
+
+ if ( rc == -ERESTART )
+ {
+ page->nr_validated_ptes = i;
+- page->partial_pte = partial ?: 1;
++ /* Set 'set', retain 'general ref' */
++ page->partial_flags = partial_flags | PTF_partial_set;
+ }
+ else if ( rc == -EINTR && i )
+ {
+ page->nr_validated_ptes = i;
+- page->partial_pte = 0;
++ page->partial_flags = 0;
+ rc = -ERESTART;
+ }
+ else if ( rc < 0 && rc != -EINTR )
+@@ -1539,7 +1560,7 @@ static int alloc_l2_table(struct page_info *page, unsigned long type)
+ if ( i )
+ {
+ page->nr_validated_ptes = i;
+- page->partial_pte = 0;
++ page->partial_flags = 0;
+ current->arch.old_guest_ptpg = NULL;
+ current->arch.old_guest_table = page;
+ }
+@@ -1563,7 +1584,8 @@ static int alloc_l3_table(struct page_info *page)
+ unsigned long pfn = mfn_x(page_to_mfn(page));
+ l3_pgentry_t *pl3e;
+ unsigned int i;
+- int rc = 0, partial = page->partial_pte;
++ int rc = 0;
++ unsigned int partial_flags = page->partial_flags;
+
+ pl3e = map_domain_page(_mfn(pfn));
+
+@@ -1578,7 +1600,7 @@ static int alloc_l3_table(struct page_info *page)
+ memset(pl3e + 4, 0, (L3_PAGETABLE_ENTRIES - 4) * sizeof(*pl3e));
+
+ for ( i = page->nr_validated_ptes; i < L3_PAGETABLE_ENTRIES;
+- i++, partial = 0 )
++ i++, partial_flags = 0 )
+ {
+ l3_pgentry_t l3e = pl3e[i];
+
+@@ -1597,7 +1619,8 @@ static int alloc_l3_table(struct page_info *page)
+ else
+ rc = get_page_and_type_from_mfn(
+ l3e_get_mfn(l3e),
+- PGT_l2_page_table | PGT_pae_xen_l2, d, partial, 1);
++ PGT_l2_page_table | PGT_pae_xen_l2, d,
++ partial_flags | PTF_preemptible);
+ }
+ else if ( !(l3e_get_flags(l3e) & _PAGE_PRESENT) )
+ {
+@@ -1606,17 +1629,18 @@ static int alloc_l3_table(struct page_info *page)
+ rc = -EINTR;
+ }
+ else
+- rc = get_page_from_l3e(l3e, pfn, d, partial);
++ rc = get_page_from_l3e(l3e, pfn, d, partial_flags);
+
+ if ( rc == -ERESTART )
+ {
+ page->nr_validated_ptes = i;
+- page->partial_pte = partial ?: 1;
++ /* Set 'set', leave 'general ref' set if this entry was set */
++ page->partial_flags = partial_flags | PTF_partial_set;
+ }
+ else if ( rc == -EINTR && i )
+ {
+ page->nr_validated_ptes = i;
+- page->partial_pte = 0;
++ page->partial_flags = 0;
+ rc = -ERESTART;
+ }
+ if ( rc < 0 )
+@@ -1633,7 +1657,7 @@ static int alloc_l3_table(struct page_info *page)
+ if ( i )
+ {
+ page->nr_validated_ptes = i;
+- page->partial_pte = 0;
++ page->partial_flags = 0;
+ current->arch.old_guest_ptpg = NULL;
+ current->arch.old_guest_table = page;
+ }
+@@ -1767,10 +1791,11 @@ static int alloc_l4_table(struct page_info *page)
+ unsigned long pfn = mfn_x(page_to_mfn(page));
+ l4_pgentry_t *pl4e = map_domain_page(_mfn(pfn));
+ unsigned int i;
+- int rc = 0, partial = page->partial_pte;
++ int rc = 0;
++ unsigned int partial_flags = page->partial_flags;
+
+ for ( i = page->nr_validated_ptes; i < L4_PAGETABLE_ENTRIES;
+- i++, partial = 0 )
++ i++, partial_flags = 0 )
+ {
+ l4_pgentry_t l4e;
+
+@@ -1786,12 +1811,13 @@ static int alloc_l4_table(struct page_info *page)
+ rc = -EINTR;
+ }
+ else
+- rc = get_page_from_l4e(l4e, pfn, d, partial);
++ rc = get_page_from_l4e(l4e, pfn, d, partial_flags);
+
+ if ( rc == -ERESTART )
+ {
+ page->nr_validated_ptes = i;
+- page->partial_pte = partial ?: 1;
++ /* Set 'set', leave 'general ref' set if this entry was set */
++ page->partial_flags = partial_flags | PTF_partial_set;
+ }
+ else if ( rc < 0 )
+ {
+@@ -1801,7 +1827,7 @@ static int alloc_l4_table(struct page_info *page)
+ if ( i )
+ {
+ page->nr_validated_ptes = i;
+- page->partial_pte = 0;
++ page->partial_flags = 0;
+ if ( rc == -EINTR )
+ rc = -ERESTART;
+ else
+@@ -1853,19 +1879,20 @@ static int free_l2_table(struct page_info *page)
+ struct domain *d = page_get_owner(page);
+ unsigned long pfn = mfn_x(page_to_mfn(page));
+ l2_pgentry_t *pl2e;
+- int rc = 0, partial = page->partial_pte;
+- unsigned int i = page->nr_validated_ptes - !partial;
++ int rc = 0;
++ unsigned int partial_flags = page->partial_flags,
++ i = page->nr_validated_ptes - !(partial_flags & PTF_partial_set);
+
+ pl2e = map_domain_page(_mfn(pfn));
+
+ for ( ; ; )
+ {
+ if ( is_guest_l2_slot(d, page->u.inuse.type_info, i) )
+- rc = put_page_from_l2e(pl2e[i], pfn, partial, false);
++ rc = put_page_from_l2e(pl2e[i], pfn, partial_flags);
+ if ( rc < 0 )
+ break;
+
+- partial = 0;
++ partial_flags = 0;
+
+ if ( !i-- )
+ break;
+@@ -1887,12 +1914,14 @@ static int free_l2_table(struct page_info *page)
+ else if ( rc == -ERESTART )
+ {
+ page->nr_validated_ptes = i;
+- page->partial_pte = partial ?: -1;
++ page->partial_flags = (partial_flags & PTF_partial_set) ?
++ partial_flags :
++ (PTF_partial_set | PTF_partial_general_ref);
+ }
+ else if ( rc == -EINTR && i < L2_PAGETABLE_ENTRIES - 1 )
+ {
+ page->nr_validated_ptes = i + 1;
+- page->partial_pte = 0;
++ page->partial_flags = 0;
+ rc = -ERESTART;
+ }
+
+@@ -1904,18 +1933,19 @@ static int free_l3_table(struct page_info *page)
+ struct domain *d = page_get_owner(page);
+ unsigned long pfn = mfn_x(page_to_mfn(page));
+ l3_pgentry_t *pl3e;
+- int rc = 0, partial = page->partial_pte;
+- unsigned int i = page->nr_validated_ptes - !partial;
++ int rc = 0;
++ unsigned int partial_flags = page->partial_flags,
++ i = page->nr_validated_ptes - !(partial_flags & PTF_partial_set);
+
+ pl3e = map_domain_page(_mfn(pfn));
+
+ for ( ; ; )
+ {
+- rc = put_page_from_l3e(pl3e[i], pfn, partial, 0);
++ rc = put_page_from_l3e(pl3e[i], pfn, partial_flags);
+ if ( rc < 0 )
+ break;
+
+- partial = 0;
++ partial_flags = 0;
+ if ( rc == 0 )
+ pl3e[i] = unadjust_guest_l3e(pl3e[i], d);
+
+@@ -1934,12 +1964,14 @@ static int free_l3_table(struct page_info *page)
+ if ( rc == -ERESTART )
+ {
+ page->nr_validated_ptes = i;
+- page->partial_pte = partial ?: -1;
++ page->partial_flags = (partial_flags & PTF_partial_set) ?
++ partial_flags :
++ (PTF_partial_set | PTF_partial_general_ref);
+ }
+ else if ( rc == -EINTR && i < L3_PAGETABLE_ENTRIES - 1 )
+ {
+ page->nr_validated_ptes = i + 1;
+- page->partial_pte = 0;
++ page->partial_flags = 0;
+ rc = -ERESTART;
+ }
+ return rc > 0 ? 0 : rc;
+@@ -1950,26 +1982,29 @@ static int free_l4_table(struct page_info *page)
+ struct domain *d = page_get_owner(page);
+ unsigned long pfn = mfn_x(page_to_mfn(page));
+ l4_pgentry_t *pl4e = map_domain_page(_mfn(pfn));
+- int rc = 0, partial = page->partial_pte;
+- unsigned int i = page->nr_validated_ptes - !partial;
++ int rc = 0;
++ unsigned partial_flags = page->partial_flags,
++ i = page->nr_validated_ptes - !(partial_flags & PTF_partial_set);
+
+ do {
+ if ( is_guest_l4_slot(d, i) )
+- rc = put_page_from_l4e(pl4e[i], pfn, partial, 0);
++ rc = put_page_from_l4e(pl4e[i], pfn, partial_flags);
+ if ( rc < 0 )
+ break;
+- partial = 0;
++ partial_flags = 0;
+ } while ( i-- );
+
+ if ( rc == -ERESTART )
+ {
+ page->nr_validated_ptes = i;
+- page->partial_pte = partial ?: -1;
++ page->partial_flags = (partial_flags & PTF_partial_set) ?
++ partial_flags :
++ (PTF_partial_set | PTF_partial_general_ref);
+ }
+ else if ( rc == -EINTR && i < L4_PAGETABLE_ENTRIES - 1 )
+ {
+ page->nr_validated_ptes = i + 1;
+- page->partial_pte = 0;
++ page->partial_flags = 0;
+ rc = -ERESTART;
+ }
+
+@@ -2247,7 +2282,7 @@ static int mod_l2_entry(l2_pgentry_t *pl2e,
+ return -EBUSY;
+ }
+
+- put_page_from_l2e(ol2e, pfn, 0, true);
++ put_page_from_l2e(ol2e, pfn, PTF_defer);
+
+ return rc;
+ }
+@@ -2315,7 +2350,7 @@ static int mod_l3_entry(l3_pgentry_t *pl3e,
+ if ( !create_pae_xen_mappings(d, pl3e) )
+ BUG();
+
+- put_page_from_l3e(ol3e, pfn, 0, 1);
++ put_page_from_l3e(ol3e, pfn, PTF_defer);
+ return rc;
+ }
+
+@@ -2378,7 +2413,7 @@ static int mod_l4_entry(l4_pgentry_t *pl4e,
+ return -EFAULT;
+ }
+
+- put_page_from_l4e(ol4e, pfn, 0, 1);
++ put_page_from_l4e(ol4e, pfn, PTF_defer);
+ return rc;
+ }
+ #endif /* CONFIG_PV */
+@@ -2649,7 +2684,7 @@ int free_page_type(struct page_info *page, unsigned long type,
+ if ( !(type & PGT_partial) )
+ {
+ page->nr_validated_ptes = 1U << PAGETABLE_ORDER;
+- page->partial_pte = 0;
++ page->partial_flags = 0;
+ }
+
+ switch ( type & PGT_type_mask )
+@@ -2946,7 +2981,7 @@ static int _get_page_type(struct page_info *page, unsigned long type,
+ if ( !(x & PGT_partial) )
+ {
+ page->nr_validated_ptes = 0;
+- page->partial_pte = 0;
++ page->partial_flags = 0;
+ }
+ page->linear_pt_count = 0;
+ rc = alloc_page_type(page, type, preemptible);
+@@ -3122,7 +3157,7 @@ int new_guest_cr3(mfn_t mfn)
+ return 0;
+ }
+
+- rc = get_page_and_type_from_mfn(mfn, PGT_root_page_table, d, 0, 1);
++ rc = get_page_and_type_from_mfn(mfn, PGT_root_page_table, d, PTF_preemptible);
+ switch ( rc )
+ {
+ case 0:
+@@ -3473,7 +3508,7 @@ long do_mmuext_op(
+ if ( op.arg1.mfn != 0 )
+ {
+ rc = get_page_and_type_from_mfn(
+- _mfn(op.arg1.mfn), PGT_root_page_table, currd, 0, 1);
++ _mfn(op.arg1.mfn), PGT_root_page_table, currd, PTF_preemptible);
+
+ if ( unlikely(rc) )
+ {
+diff --git a/xen/include/asm-x86/mm.h b/xen/include/asm-x86/mm.h
+index 6faa563167..8406ac3c37 100644
+--- a/xen/include/asm-x86/mm.h
++++ b/xen/include/asm-x86/mm.h
+@@ -228,19 +228,34 @@ struct page_info
+ * setting the flag must not drop that reference, whereas the instance
+ * clearing it will have to.
+ *
+- * If @partial_pte is positive then PTE at @nr_validated_ptes+1 has
+- * been partially validated. This implies that the general reference
+- * to the page (acquired from get_page_from_lNe()) would be dropped
+- * (again due to the apparent failure) and hence must be re-acquired
+- * when resuming the validation, but must not be dropped when picking
+- * up the page for invalidation.
++ * If partial_flags & PTF_partial_set is set, then the page at
++ * at @nr_validated_ptes had PGT_partial set as a result of an
++ * operation on the current page. (That page may or may not
++ * still have PGT_partial set.)
+ *
+- * If @partial_pte is negative then PTE at @nr_validated_ptes+1 has
+- * been partially invalidated. This is basically the opposite case of
+- * above, i.e. the general reference to the page was not dropped in
+- * put_page_from_lNe() (due to the apparent failure), and hence it
+- * must be dropped when the put operation is resumed (and completes),
+- * but it must not be acquired if picking up the page for validation.
++ * If PTF_partial_general_ref is set, then the PTE at
++ * @nr_validated_ptef holds a general reference count for the
++ * page.
++ *
++ * This happens:
++ * - During de-validation, if de-validation of the page was
++ * interrupted
++ * - During validation, if an invalid entry is encountered and
++ * validation is preemptible
++ * - During validation, if PTF_partial_general_ref was set on
++ * this entry to begin with (perhaps because we're picking
++ * up from a partial de-validation).
++ *
++ * When resuming validation, if PTF_partial_general_ref is clear,
++ * then a general reference must be re-acquired; if it is set, no
++ * reference should be acquired.
++ *
++ * When resuming de-validation, if PTF_partial_general_ref is
++ * clear, no reference should be dropped; if it is set, a
++ * reference should be dropped.
++ *
++ * NB that PTF_partial_set and PTF_partial_general_ref are
++ * defined in mm.c, the only place where they are used.
+ *
+ * The 3rd field, @linear_pt_count, indicates
+ * - by a positive value, how many same-level page table entries a page
+@@ -251,7 +266,7 @@ struct page_info
+ struct {
+ u16 nr_validated_ptes:PAGETABLE_ORDER + 1;
+ u16 :16 - PAGETABLE_ORDER - 1 - 2;
+- s16 partial_pte:2;
++ u16 partial_flags:2;
+ s16 linear_pt_count;
+ };
+
+--
+2.23.0
+
generated by cgit v1.2.3 (git 2.26.2) at 2024-12-12 20:32:09 +0000