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powerpc/64s: Fix compiler store ordering to SLB shadow area

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The stores to update the SLB shadow area must be made as they appear
in the C code, so that the hypervisor does not see an entry with
mismatched vsid and esid. Use WRITE_ONCE for this.

GCC has been observed to elide the first store to esid in the update,
which means that if the hypervisor interrupts the guest after storing
to vsid, it could see an entry with old esid and new vsid, which may
possibly result in memory corruption.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Nicholas Piggin 2018-05-30 20:31:22 +10:00 committed by Michael Ellerman
parent 0cef77c779
commit 926bc2f100
1 changed files with 4 additions and 4 deletions
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8
arch/powerpc/mm/slb.c
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@ -63,14 +63,14 @@ static inline void slb_shadow_update(unsigned long ea, int ssize,
* updating it. No write barriers are needed here, provided
* we only update the current CPU's SLB shadow buffer.
*/
p->save_area[index].esid = 0;
p->save_area[index].vsid = cpu_to_be64(mk_vsid_data(ea, ssize, flags));
p->save_area[index].esid = cpu_to_be64(mk_esid_data(ea, ssize, index));
WRITE_ONCE(p->save_area[index].esid, 0);
WRITE_ONCE(p->save_area[index].vsid, cpu_to_be64(mk_vsid_data(ea, ssize, flags)));
WRITE_ONCE(p->save_area[index].esid, cpu_to_be64(mk_esid_data(ea, ssize, index)));
}
static inline void slb_shadow_clear(enum slb_index index)
{
get_slb_shadow()->save_area[index].esid = 0;
WRITE_ONCE(get_slb_shadow()->save_area[index].esid, 0);
}
static inline void create_shadowed_slbe(unsigned long ea, int ssize,