File xsa380-0.patch of Package xen.23693
# Commit 921f1f42260c7967bf18f8a143d39511d163c421
# Date 2019-12-03 14:13:40 +0100
# Author Jan Beulich <jbeulich@suse.com>
# Committer Jan Beulich <jbeulich@suse.com>
gnttab: make sure grant map operations don't skip their IOMMU part
Two almost simultaneous mapping requests need to make sure that at the
completion of the earlier one IOMMU mappings (established explicitly
here in the PV case) have been put in place. Forever since the splitting
of the grant table lock a violation of this has been possible (using
simplified pin counts, as it doesn't matter whether we talk about read
or write mappings here):
initial state: act->pin = 0
vCPU A: progress the operation past the dropping of the locks after the
act->pin updates (act->pin = 1, old_pin = 0, act_pin = 1)
vCPU B: progress the operation past the dropping of the locks after the
act->pin updates (act->pin = 2, old_pin = 1, act_pin = 2)
vCPU B: (re-)acquire both gt locks, mapkind() returns 0, but both
iommu_legacy_map() invocations get skipped due to non-zero
old_pin
vCPU B: return to caller without IOMMU mapping
vCPU A: (re-)acquire both gt locks, mapkind() returns 0,
iommu_legacy_map() gets invoked
With the locks dropped intermediately, whether to invoke
iommu_legacy_map() must depend on only the return value of mapkind()
and of course the kind of mapping request being processed, just like
is already the case in unmap_common().
Also fix the style of the adjacent comment, and correct a nearby one
still referring to a prior name of what is now mapkind().
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
--- a/xen/common/grant_table.c
+++ b/xen/common/grant_table.c
@@ -918,8 +918,6 @@ map_grant_ref(
unsigned long frame = 0;
struct page_info *pg = NULL;
int rc = GNTST_okay;
- u32 old_pin;
- u32 act_pin;
unsigned int cache_flags, refcnt = 0, typecnt = 0;
bool host_map_created = false;
struct active_grant_entry *act = NULL;
@@ -1023,7 +1021,6 @@ map_grant_ref(
}
}
- old_pin = act->pin;
if ( op->flags & GNTMAP_device_map )
act->pin += (op->flags & GNTMAP_readonly) ?
GNTPIN_devr_inc : GNTPIN_devw_inc;
@@ -1032,7 +1029,6 @@ map_grant_ref(
GNTPIN_hstr_inc : GNTPIN_hstw_inc;
frame = act->frame;
- act_pin = act->pin;
cache_flags = (shah->flags & (GTF_PAT | GTF_PWT | GTF_PCD) );
@@ -1140,26 +1136,22 @@ map_grant_ref(
if ( need_iommu )
{
unsigned int kind;
- int err = 0;
double_gt_lock(lgt, rgt);
- /* We're not translated, so we know that gmfns and mfns are
- the same things, so the IOMMU entry is always 1-to-1. */
+ /*
+ * We're not translated, so we know that dfns and mfns are
+ * the same things, so the IOMMU entry is always 1-to-1.
+ */
kind = mapkind(lgt, rd, frame);
- if ( (act_pin & (GNTPIN_hstw_mask|GNTPIN_devw_mask)) &&
- !(old_pin & (GNTPIN_hstw_mask|GNTPIN_devw_mask)) )
- {
- if ( !(kind & MAPKIND_WRITE) )
- err = iommu_map_page(ld, frame, frame,
- IOMMUF_readable|IOMMUF_writable);
- }
- else if ( act_pin && !old_pin )
- {
- if ( !kind )
- err = iommu_map_page(ld, frame, frame, IOMMUF_readable);
- }
- if ( err )
+ if ( !(op->flags & GNTMAP_readonly) &&
+ !(kind & MAPKIND_WRITE) )
+ kind = IOMMUF_readable | IOMMUF_writable;
+ else if ( !kind )
+ kind = IOMMUF_readable;
+ else
+ kind = 0;
+ if ( kind && iommu_map_page(ld, frame, frame, kind) )
{
double_gt_unlock(lgt, rgt);
rc = GNTST_general_error;
@@ -1174,7 +1166,7 @@ map_grant_ref(
* other fields so just ensure the flags field is stored last.
*
* However, if gnttab_need_iommu_mapping() then this would race
- * with a concurrent mapcount() call (on an unmap, for example)
+ * with a concurrent mapkind() call (on an unmap, for example)
* and a lock is required.
*/
mt = &maptrack_entry(lgt, handle);