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Increment page reference count for every host/device

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mapping created via a grant reference, rather than one
increment for all uses of a single grant reference.
This avoids a nasty situation in put_page_from_l1e()
where we cannot reliably determine whether a mapping was
created via a grant reference and so we must always
decrement the mapped page's reference count.

Signed-off-by: Keir Fraser <keir@xensource.com>
This commit is contained in:
kaf24@firebug.cl.cam.ac.uk committed 2005-12-21 18:25:34 +01:00
1 parent f1e0d84148
commit d9af6ba2e0
1 file changed
+93 -150
Download Patch File Download Diff File Expand all files Collapse all files
xen/common/grant_table.c
+93 -150
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@@ -177,17 +177,19 @@ __gnttab_map_grant_ref(
spin_lock(&rd->grant_table->lock);
if ( act->pin == 0 )
if ( !act->pin ||
(!(dev_hst_ro_flags & GNTMAP_readonly) &&
!(act->pin & (GNTPIN_hstw_mask|GNTPIN_devw_mask))) )
{
/* CASE 1: Activating a previously inactive entry. */
sflags = sha->flags;
sdom = sha->domid;
/* This loop attempts to set the access (reading/writing) flags
/*
* This loop attempts to set the access (reading/writing) flags
* in the grant table entry. It tries a cmpxchg on the field
* up to five times, and then fails under the assumption that
* the guest is misbehaving. */
* the guest is misbehaving.
*/
for ( ; ; )
{
u32 scombo, prev_scombo, new_scombo;
@@ -196,7 +198,7 @@ __gnttab_map_grant_ref(
unlikely(sdom != led->domain->domain_id) )
PIN_FAIL(unlock_out, GNTST_general_error,
"Bad flags (%x) or dom (%d). (NB. expected dom %d)\n",
sflags, sdom, led->domain->domain_id);
sflags, sdom, led->domain->domain_id);
/* Merge two 16-bit values into a 32-bit combined update. */
/* NB. Endianness! */
@@ -232,132 +234,50 @@ __gnttab_map_grant_ref(
sdom = (u16)(prev_scombo >> 16);
}
/* rmb(); */ /* not on x86 */
frame = __gpfn_to_mfn(rd, sha->frame);
if ( unlikely(!pfn_valid(frame)) ||
unlikely(!((dev_hst_ro_flags & GNTMAP_readonly) ?
get_page(pfn_to_page(frame), rd) :
get_page_and_type(pfn_to_page(frame), rd,
PGT_writable_page))) )
if ( !act->pin )
{
clear_bit(_GTF_writing, &sha->flags);
clear_bit(_GTF_reading, &sha->flags);
PIN_FAIL(unlock_out, GNTST_general_error,
"Could not pin the granted frame (%lx)!\n", frame);
act->domid = sdom;
act->frame = __gpfn_to_mfn(rd, sha->frame);
}
if ( dev_hst_ro_flags & GNTMAP_device_map )
act->pin += (dev_hst_ro_flags & GNTMAP_readonly) ?
GNTPIN_devr_inc : GNTPIN_devw_inc;
if ( dev_hst_ro_flags & GNTMAP_host_map )
act->pin += (dev_hst_ro_flags & GNTMAP_readonly) ?
GNTPIN_hstr_inc : GNTPIN_hstw_inc;
act->domid = sdom;
act->frame = frame;
}
else
{
/* CASE 2: Active modications to an already active entry. */
else if ( (act->pin & 0x80808080U) != 0 )
PIN_FAIL(unlock_out, ENOSPC,
"Risk of counter overflow %08x\n", act->pin);
/*
* A cheesy check for possible pin-count overflow.
* A more accurate check cannot be done with a single comparison.
*/
if ( (act->pin & 0x80808080U) != 0 )
PIN_FAIL(unlock_out, ENOSPC,
"Risk of counter overflow %08x\n", act->pin);
sflags = sha->flags;
frame = act->frame;
if ( !(dev_hst_ro_flags & GNTMAP_readonly) &&
!(act->pin & (GNTPIN_hstw_mask|GNTPIN_devw_mask)) )
{
for ( ; ; )
{
u16 prev_sflags;
if ( unlikely(sflags & GTF_readonly) )
PIN_FAIL(unlock_out, GNTST_general_error,
"Attempt to write-pin a r/o grant entry.\n");
prev_sflags = sflags;
/* NB. prev_sflags is updated in place to seen value. */
if ( unlikely(cmpxchg_user(&sha->flags, prev_sflags,
prev_sflags | GTF_writing)) )
PIN_FAIL(unlock_out, GNTST_general_error,
"Fault while modifying shared flags.\n");
if ( likely(prev_sflags == sflags) )
break;
if ( retries++ == 4 )
PIN_FAIL(unlock_out, GNTST_general_error,
"Shared grant entry is unstable.\n");
sflags = prev_sflags;
}
if ( unlikely(!get_page_type(pfn_to_page(frame),
PGT_writable_page)) )
{
clear_bit(_GTF_writing, &sha->flags);
PIN_FAIL(unlock_out, GNTST_general_error,
"Attempt to write-pin a unwritable page.\n");
}
}
if ( dev_hst_ro_flags & GNTMAP_device_map )
act->pin += (dev_hst_ro_flags & GNTMAP_readonly) ?
GNTPIN_devr_inc : GNTPIN_devw_inc;
if ( dev_hst_ro_flags & GNTMAP_host_map )
act->pin += (dev_hst_ro_flags & GNTMAP_readonly) ?
GNTPIN_hstr_inc : GNTPIN_hstw_inc;
}
/*
* At this point:
* act->pin updated to reference count mappings.
* sha->flags updated to indicate to granting domain mapping done.
* frame contains the mfn.
*/
if ( dev_hst_ro_flags & GNTMAP_device_map )
act->pin += (dev_hst_ro_flags & GNTMAP_readonly) ?
GNTPIN_devr_inc : GNTPIN_devw_inc;
if ( dev_hst_ro_flags & GNTMAP_host_map )
act->pin += (dev_hst_ro_flags & GNTMAP_readonly) ?
GNTPIN_hstr_inc : GNTPIN_hstw_inc;
spin_unlock(&rd->grant_table->lock);
frame = act->frame;
if ( unlikely(!pfn_valid(frame)) ||
unlikely(!((dev_hst_ro_flags & GNTMAP_readonly) ?
get_page(pfn_to_page(frame), rd) :
get_page_and_type(pfn_to_page(frame), rd,
PGT_writable_page))) )
PIN_FAIL(undo_out, GNTST_general_error,
"Could not pin the granted frame (%lx)!\n", frame);
if ( dev_hst_ro_flags & GNTMAP_host_map )
{
rc = create_grant_host_mapping(addr, frame, dev_hst_ro_flags);
if ( rc < 0 )
if ( rc != GNTST_okay )
{
/* Failure: undo and abort. */
if ( !(dev_hst_ro_flags & GNTMAP_readonly) )
put_page_type(pfn_to_page(frame));
put_page(pfn_to_page(frame));
goto undo_out;
}
spin_lock(&rd->grant_table->lock);
if ( dev_hst_ro_flags & GNTMAP_readonly )
{
act->pin -= GNTPIN_hstr_inc;
}
else
{
act->pin -= GNTPIN_hstw_inc;
if ( (act->pin & (GNTPIN_hstw_mask|GNTPIN_devw_mask)) == 0 )
{
clear_bit(_GTF_writing, &sha->flags);
put_page_type(pfn_to_page(frame));
}
}
if ( act->pin == 0 )
{
clear_bit(_GTF_reading, &sha->flags);
put_page(pfn_to_page(frame));
}
spin_unlock(&rd->grant_table->lock);
if ( dev_hst_ro_flags & GNTMAP_device_map )
{
(void)get_page(pfn_to_page(frame), rd);
if ( !(dev_hst_ro_flags & GNTMAP_readonly) )
get_page_type(pfn_to_page(frame), PGT_writable_page);
}
}
@@ -375,6 +295,24 @@ __gnttab_map_grant_ref(
put_domain(rd);
return rc;
undo_out:
spin_lock(&rd->grant_table->lock);
if ( dev_hst_ro_flags & GNTMAP_device_map )
act->pin -= (dev_hst_ro_flags & GNTMAP_readonly) ?
GNTPIN_devr_inc : GNTPIN_devw_inc;
if ( dev_hst_ro_flags & GNTMAP_host_map )
act->pin -= (dev_hst_ro_flags & GNTMAP_readonly) ?
GNTPIN_hstr_inc : GNTPIN_hstw_inc;
if ( !(dev_hst_ro_flags & GNTMAP_readonly) &&
!(act->pin & (GNTPIN_hstw_mask|GNTPIN_devw_mask)) )
clear_bit(_GTF_writing, &sha->flags);
if ( !act->pin )
clear_bit(_GTF_reading, &sha->flags);
spin_unlock(&rd->grant_table->lock);
unlock_out:
spin_unlock(&rd->grant_table->lock);
@@ -465,27 +403,42 @@ __gnttab_unmap_grant_ref(
PIN_FAIL(unmap_out, GNTST_general_error,
"Bad frame number doesn't match gntref.\n");
if ( flags & GNTMAP_device_map )
act->pin -= (flags & GNTMAP_readonly) ? GNTPIN_devr_inc
: GNTPIN_devw_inc;
map->ref_and_flags &= ~GNTMAP_device_map;
(void)__put_user(0, &uop->dev_bus_addr);
{
ASSERT(act->pin & (GNTPIN_devw_mask | GNTPIN_devr_mask));
map->ref_and_flags &= ~GNTMAP_device_map;
if ( flags & GNTMAP_readonly )
{
act->pin -= GNTPIN_devr_inc;
put_page(pfn_to_page(frame));
}
else
{
act->pin -= GNTPIN_devw_inc;
put_page_and_type(pfn_to_page(frame));
}
}
}
if ( (addr != 0) &&
(flags & GNTMAP_host_map) &&
((act->pin & (GNTPIN_hstw_mask | GNTPIN_hstr_mask)) > 0))
if ( (addr != 0) && (flags & GNTMAP_host_map) )
{
if ( (rc = destroy_grant_host_mapping(addr, frame, flags)) < 0 )
goto unmap_out;
ASSERT(act->pin & (GNTPIN_hstw_mask | GNTPIN_hstr_mask));
map->ref_and_flags &= ~GNTMAP_host_map;
act->pin -= (flags & GNTMAP_readonly) ? GNTPIN_hstr_inc
: GNTPIN_hstw_inc;
if ( flags & GNTMAP_readonly )
{
act->pin -= GNTPIN_hstr_inc;
put_page(pfn_to_page(frame));
}
else
{
act->pin -= GNTPIN_hstw_inc;
put_page_and_type(pfn_to_page(frame));
}
}
if ( (map->ref_and_flags & (GNTMAP_device_map|GNTMAP_host_map)) == 0)
if ( (map->ref_and_flags & (GNTMAP_device_map|GNTMAP_host_map)) == 0 )
{
map->ref_and_flags = 0;
put_maptrack_handle(ld->grant_table, handle);
@@ -495,20 +448,12 @@ __gnttab_unmap_grant_ref(
if ( !(flags & GNTMAP_readonly) )
gnttab_log_dirty(rd, frame);
/* If the last writable mapping has been removed, put_page_type */
if ( ((act->pin & (GNTPIN_devw_mask|GNTPIN_hstw_mask)) == 0) &&
!(flags & GNTMAP_readonly) )
{
clear_bit(_GTF_writing, &sha->flags);
put_page_type(pfn_to_page(frame));
}
if ( act->pin == 0 )
{
act->frame = 0xdeadbeef;
clear_bit(_GTF_reading, &sha->flags);
put_page(pfn_to_page(frame));
}
unmap_out:
(void)__put_user(rc, &uop->status);
@@ -989,42 +934,40 @@ gnttab_release_mappings(
{
if ( map->ref_and_flags & GNTMAP_device_map )
{
BUG_ON((act->pin & GNTPIN_devr_mask) == 0);
BUG_ON(!(act->pin & GNTPIN_devr_mask));
act->pin -= GNTPIN_devr_inc;
put_page(pfn_to_page(act->frame));
}
if ( map->ref_and_flags & GNTMAP_host_map )
{
BUG_ON((act->pin & GNTPIN_hstr_mask) == 0);
BUG_ON(!(act->pin & GNTPIN_hstr_mask));
act->pin -= GNTPIN_hstr_inc;
put_page(pfn_to_page(act->frame));
}
}
else
{
if ( map->ref_and_flags & GNTMAP_device_map )
{
BUG_ON((act->pin & GNTPIN_devw_mask) == 0);
BUG_ON(!(act->pin & GNTPIN_devw_mask));
act->pin -= GNTPIN_devw_inc;
put_page_and_type(pfn_to_page(act->frame));
}
if ( map->ref_and_flags & GNTMAP_host_map )
{
BUG_ON((act->pin & GNTPIN_hstw_mask) == 0);
BUG_ON(!(act->pin & GNTPIN_hstw_mask));
act->pin -= GNTPIN_hstw_inc;
put_page_and_type(pfn_to_page(act->frame));
}
if ( (act->pin & (GNTPIN_devw_mask|GNTPIN_hstw_mask)) == 0 )
{
clear_bit(_GTF_writing, &sha->flags);
put_page_type(pfn_to_page(act->frame));
}
}
if ( act->pin == 0 )
{
clear_bit(_GTF_reading, &sha->flags);
put_page(pfn_to_page(act->frame));
}
spin_unlock(&rd->grant_table->lock);
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