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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-changelog] [xen stable-4.8] x86/mm: also allow L2 (un)validation to be fully preemptible
commit 51c3b69d730c11681174a16c1dd96b99216ab427
Author: Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue Mar 5 15:42:32 2019 +0100
Commit: Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Mar 5 15:42:32 2019 +0100
x86/mm: also allow L2 (un)validation to be fully preemptible
Commit c612481d1c ("x86/mm: Plumbing to allow any PTE update to fail
with -ERESTART") added assertions next to the {alloc,free}_l2_table()
invocations to document (and validate in debug builds) that L2
(un)validations are always preemptible.
The assertion in free_page_type() was now observed to trigger when
recursive L2 page tables get cleaned up.
In particular put_page_from_l2e()'s assumption that _put_page_type()
would always succeed is now wrong, resulting in a partially un-validated
page left in a domain, which has no other means of getting cleaned up
later on. If not causing any problems earlier, this would ultimately
trigger the check for ->u.inuse.type_info having a zero count when
freeing the page during cleanup after the domain has died.
As a result it should be considered a mistake to not have extended
preemption fully to L2 when it was added to L3/L4 table handling, which
this change aims to correct.
The validation side additions are done just for symmetry.
This is part of XSA-290.
Reported-by: Manuel Bouyer <bouyer@xxxxxxxxxxxxxxx>
Tested-by: Manuel Bouyer <bouyer@xxxxxxxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
master commit: 176ebf9c8bc2828f6637eb61cc1cf166e302c699
master date: 2019-03-05 13:51:18 +0100
---
xen/arch/x86/mm.c | 116 +++++++++++++++++++++++++++++++++++++++---------------
1 file changed, 84 insertions(+), 32 deletions(-)
diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 9f375bc236..91a162923a 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -1240,7 +1240,7 @@ get_page_from_l1e(
define_get_linear_pagetable(l2);
static int
get_page_from_l2e(
- l2_pgentry_t l2e, unsigned long pfn, struct domain *d)
+ l2_pgentry_t l2e, unsigned long pfn, struct domain *d, int partial)
{
unsigned long mfn = l2e_get_pfn(l2e);
int rc;
@@ -1256,7 +1256,8 @@ get_page_from_l2e(
if ( !(l2e_get_flags(l2e) & _PAGE_PSE) )
{
- rc = get_page_and_type_from_pagenr(mfn, PGT_l1_page_table, d, 0, 0);
+ rc = get_page_and_type_from_pagenr(mfn, PGT_l1_page_table, d,
+ partial, false);
if ( unlikely(rc == -EINVAL) && get_l2_linear_pagetable(l2e, pfn, d) )
rc = 0;
return rc;
@@ -1451,8 +1452,11 @@ void put_page_from_l1e(l1_pgentry_t l1e, struct domain
*l1e_owner)
* NB. Virtual address 'l2e' maps to a machine address within frame 'pfn'.
* 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)
+static int put_page_from_l2e(l2_pgentry_t l2e, unsigned long pfn,
+ int partial, bool defer)
{
+ int rc = 0;
+
if ( !(l2e_get_flags(l2e) & _PAGE_PRESENT) || (l2e_get_pfn(l2e) == pfn) )
return 1;
@@ -1461,13 +1465,27 @@ static int put_page_from_l2e(l2_pgentry_t l2e, unsigned
long pfn)
else
{
struct page_info *pg = l2e_get_page(l2e);
- int rc = _put_page_type(pg, false, mfn_to_page(pfn));
+ struct page_info *ptpg = mfn_to_page(pfn);
- ASSERT(!rc);
- put_page(pg);
+ if ( unlikely(partial > 0) )
+ {
+ ASSERT(!defer);
+ rc = _put_page_type(pg, true, ptpg);
+ }
+ else if ( defer )
+ {
+ current->arch.old_guest_ptpg = ptpg;
+ current->arch.old_guest_table = pg;
+ }
+ else
+ {
+ rc = _put_page_type(pg, true, ptpg);
+ if ( likely(!rc) )
+ put_page(pg);
+ }
}
- return 0;
+ return rc;
}
static int put_page_from_l3e(l3_pgentry_t l3e, unsigned long pfn,
@@ -1640,11 +1658,12 @@ static int alloc_l2_table(struct page_info *page,
unsigned long type)
unsigned long pfn = page_to_mfn(page);
l2_pgentry_t *pl2e;
unsigned int i;
- int rc = 0;
+ int rc = 0, partial = page->partial_pte;
pl2e = map_domain_page(_mfn(pfn));
- for ( i = page->nr_validated_ptes; i < L2_PAGETABLE_ENTRIES; i++ )
+ for ( i = page->nr_validated_ptes; i < L2_PAGETABLE_ENTRIES;
+ i++, partial = 0 )
{
if ( i > page->nr_validated_ptes && hypercall_preempt_check() )
{
@@ -1654,23 +1673,33 @@ static int alloc_l2_table(struct page_info *page,
unsigned long type)
}
if ( !is_guest_l2_slot(d, type, i) ||
- (rc = get_page_from_l2e(pl2e[i], pfn, d)) > 0 )
+ (rc = get_page_from_l2e(pl2e[i], pfn, d, partial)) > 0 )
continue;
- if ( unlikely(rc == -ERESTART) )
+ if ( rc == -ERESTART )
{
page->nr_validated_ptes = i;
- break;
+ page->partial_pte = partial ?: 1;
}
-
- if ( rc < 0 )
+ else if ( rc == -EINTR && i )
+ {
+ page->nr_validated_ptes = i;
+ page->partial_pte = 0;
+ rc = -ERESTART;
+ }
+ else if ( rc < 0 && rc != -EINTR )
{
MEM_LOG("Failure in alloc_l2_table: entry %d", i);
- while ( i-- > 0 )
- if ( is_guest_l2_slot(d, type, i) )
- put_page_from_l2e(pl2e[i], pfn);
- break;
+ if ( i )
+ {
+ page->nr_validated_ptes = i;
+ page->partial_pte = 0;
+ current->arch.old_guest_ptpg = NULL;
+ current->arch.old_guest_table = page;
+ }
}
+ if ( rc < 0 )
+ break;
adjust_guest_l2e(pl2e[i], d);
}
@@ -1892,28 +1921,50 @@ static int free_l2_table(struct page_info *page)
struct domain *d = page_get_owner(page);
unsigned long pfn = page_to_mfn(page);
l2_pgentry_t *pl2e;
- unsigned int i = page->nr_validated_ptes - 1;
- int err = 0;
+ int rc = 0, partial = page->partial_pte;
+ unsigned int i = page->nr_validated_ptes - !partial;
pl2e = map_domain_page(_mfn(pfn));
- ASSERT(page->nr_validated_ptes);
- do {
- if ( is_guest_l2_slot(d, page->u.inuse.type_info, i) &&
- put_page_from_l2e(pl2e[i], pfn) == 0 &&
- i && hypercall_preempt_check() )
+ for ( ; ; )
+ {
+ if ( is_guest_l2_slot(d, page->u.inuse.type_info, i) )
+ rc = put_page_from_l2e(pl2e[i], pfn, partial, false);
+ if ( rc < 0 )
+ break;
+
+ partial = 0;
+
+ if ( !i-- )
+ break;
+
+ if ( hypercall_preempt_check() )
{
- page->nr_validated_ptes = i;
- err = -ERESTART;
+ rc = -EINTR;
+ break;
}
- } while ( !err && i-- );
+ }
unmap_domain_page(pl2e);
- if ( !err )
+ if ( rc >= 0 )
+ {
page->u.inuse.type_info &= ~PGT_pae_xen_l2;
+ rc = 0;
+ }
+ else if ( rc == -ERESTART )
+ {
+ page->nr_validated_ptes = i;
+ page->partial_pte = partial ?: -1;
+ }
+ else if ( rc == -EINTR && i < L2_PAGETABLE_ENTRIES - 1 )
+ {
+ page->nr_validated_ptes = i + 1;
+ page->partial_pte = 0;
+ rc = -ERESTART;
+ }
- return err;
+ return rc;
}
static int free_l3_table(struct page_info *page)
@@ -2238,7 +2289,7 @@ static int mod_l2_entry(l2_pgentry_t *pl2e,
return -EBUSY;
}
- if ( unlikely((rc = get_page_from_l2e(nl2e, pfn, d)) < 0) )
+ if ( unlikely((rc = get_page_from_l2e(nl2e, pfn, d, 0)) < 0) )
return rc;
adjust_guest_l2e(nl2e, d);
@@ -2257,7 +2308,8 @@ static int mod_l2_entry(l2_pgentry_t *pl2e,
return -EBUSY;
}
- put_page_from_l2e(ol2e, pfn);
+ put_page_from_l2e(ol2e, pfn, 0, true);
+
return rc;
}
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.8
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