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[XEN] grant tables: update pair of entries using a union to ensure endian neutrality.
The first two members of a grant entry are updated as a combined pair. The following patch uses a union so updates can happen in an endian neutral fashion. Signed-off-by: Jimi Xenidis <jimix@watson.ibm.com>
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kfraser@localhost.localdomain committed
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+49
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@@ -33,6 +33,18 @@
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#include <xen/domain_page.h>
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#include <acm/acm_hooks.h>
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/*
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* The first two members of a grant entry are updated as a combined pair.
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* The following union allows that to happen in an endian-neutral fashion.
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*/
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union grant_combo {
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uint32_t word;
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struct {
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uint16_t flags;
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domid_t domid;
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} shorts;
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};
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#define PIN_FAIL(_lbl, _rc, _f, _a...) \
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do { \
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DPRINTK( _f, ## _a ); \
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@@ -178,7 +190,7 @@ __gnttab_map_grant_ref(
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*/
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for ( ; ; )
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{
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u32 scombo, prev_scombo, new_scombo;
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union grant_combo scombo, prev_scombo, new_scombo;
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if ( unlikely((sflags & GTF_type_mask) != GTF_permit_access) ||
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unlikely(sdom != led->domain->domain_id) )
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@@ -187,22 +199,25 @@ __gnttab_map_grant_ref(
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sflags, sdom, led->domain->domain_id);
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/* Merge two 16-bit values into a 32-bit combined update. */
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/* NB. Endianness! */
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scombo = ((u32)sdom << 16) | (u32)sflags;
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scombo.shorts.flags = sflags;
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scombo.shorts.domid = sdom;
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new_scombo = scombo;
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new_scombo.shorts.flags |= GTF_reading;
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new_scombo = scombo | GTF_reading;
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if ( !(op->flags & GNTMAP_readonly) )
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{
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new_scombo |= GTF_writing;
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new_scombo.shorts.flags |= GTF_writing;
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if ( unlikely(sflags & GTF_readonly) )
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PIN_FAIL(unlock_out, GNTST_general_error,
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"Attempt to write-pin a r/o grant entry.\n");
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}
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prev_scombo = cmpxchg((u32 *)&sha->flags, scombo, new_scombo);
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prev_scombo.word = cmpxchg((u32 *)&sha->flags,
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scombo.word, new_scombo.word);
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/* Did the combined update work (did we see what we expected?). */
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if ( likely(prev_scombo == scombo) )
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if ( likely(prev_scombo.word == scombo.word) )
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break;
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if ( retries++ == 4 )
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@@ -210,9 +225,8 @@ __gnttab_map_grant_ref(
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"Shared grant entry is unstable.\n");
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/* Didn't see what we expected. Split out the seen flags & dom. */
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/* NB. Endianness! */
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sflags = (u16)prev_scombo;
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sdom = (u16)(prev_scombo >> 16);
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sflags = prev_scombo.shorts.flags;
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sdom = prev_scombo.shorts.domid;
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}
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if ( !act->pin )
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@@ -533,7 +547,7 @@ gnttab_prepare_for_transfer(
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struct grant_entry *sha;
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domid_t sdom;
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u16 sflags;
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u32 scombo, prev_scombo;
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union grant_combo scombo, prev_scombo, tmp_scombo;
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int retries = 0;
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if ( unlikely((rgt = rd->grant_table) == NULL) ||
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@@ -562,14 +576,16 @@ gnttab_prepare_for_transfer(
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}
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/* Merge two 16-bit values into a 32-bit combined update. */
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/* NB. Endianness! */
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scombo = ((u32)sdom << 16) | (u32)sflags;
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scombo.shorts.flags = sflags;
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scombo.shorts.domid = sdom;
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prev_scombo = cmpxchg((u32 *)&sha->flags, scombo,
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scombo | GTF_transfer_committed);
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tmp_scombo = scombo;
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tmp_scombo.shorts.flags |= GTF_transfer_committed;
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prev_scombo.word = cmpxchg((u32 *)&sha->flags,
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scombo.word, tmp_scombo.word);
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/* Did the combined update work (did we see what we expected?). */
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if ( likely(prev_scombo == scombo) )
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if ( likely(prev_scombo.word == scombo.word) )
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break;
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if ( retries++ == 4 )
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@@ -579,9 +595,8 @@ gnttab_prepare_for_transfer(
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}
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/* Didn't see what we expected. Split out the seen flags & dom. */
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/* NB. Endianness! */
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sflags = (u16)prev_scombo;
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sdom = (u16)(prev_scombo >> 16);
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sflags = prev_scombo.shorts.flags;
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sdom = prev_scombo.shorts.domid;
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}
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spin_unlock(&rgt->lock);
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@@ -764,33 +779,38 @@ __acquire_grant_for_copy(
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for ( ; ; )
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{
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u32 scombo;
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u32 prev_scombo;
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u32 new_scombo;
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union grant_combo scombo, prev_scombo, new_scombo;
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if ( unlikely((sflags & GTF_type_mask) != GTF_permit_access ||
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sdom != current->domain->domain_id ) )
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PIN_FAIL(unlock_out, GNTST_general_error,
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"Bad flags (%x) or dom (%d). (NB. expected dom %d)\n",
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sflags, sdom, current->domain->domain_id);
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scombo = ((u32)sdom << 16) | (u32)sflags;
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new_scombo = scombo | GTF_reading;
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/* Merge two 16-bit values into a 32-bit combined update. */
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scombo.shorts.flags = sflags;
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scombo.shorts.domid = sdom;
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new_scombo = scombo;
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new_scombo.shorts.flags |= GTF_reading;
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if ( !readonly )
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{
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new_scombo |= GTF_writing;
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new_scombo.shorts.flags |= GTF_writing;
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if ( unlikely(sflags & GTF_readonly) )
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PIN_FAIL(unlock_out, GNTST_general_error,
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"Attempt to write-pin a r/o grant entry.\n");
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}
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prev_scombo = cmpxchg((u32 *)&sha->flags, scombo, new_scombo);
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if ( likely(prev_scombo == scombo) )
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prev_scombo.word = cmpxchg((u32 *)&sha->flags,
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scombo.word, new_scombo.word);
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if ( likely(prev_scombo.word == scombo.word) )
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break;
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if ( retries++ == 4 )
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PIN_FAIL(unlock_out, GNTST_general_error,
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"Shared grant entry is unstable.\n");
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sflags = (u16)prev_scombo;
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sdom = (u16)(prev_scombo >> 16);
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sflags = prev_scombo.shorts.flags;
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sdom = prev_scombo.shorts.flags;
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}
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if ( !act->pin )
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