tjh.dev / kernel
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s390/kvm: REPLACE barrier fixup with READ_ONCE

ACCESS_ONCE does not work reliably on non-scalar types. For
example gcc 4.6 and 4.7 might remove the volatile tag for such
accesses during the SRA (scalar replacement of aggregates) step
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145)

Commit 1365039d0cb3 ("KVM: s390: Fix ipte locking") replace
ACCESS_ONCE with barriers. Lets use READ_ONCE instead.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

Christian Borntraeger 5de72a22 488beef1

options
unified split
Changed files
+6 -12
arch
s390
kvm
gaccess.c
+6 -12
arch/s390/kvm/gaccess.c
··· 229 229 goto out; 230 230 ic = &vcpu->kvm->arch.sca->ipte_control; 231 231 do { 232 - old = *ic; 233 - barrier(); 232 + old = READ_ONCE(*ic); 234 233 while (old.k) { 235 234 cond_resched(); 236 - old = *ic; 237 - barrier(); 235 + old = READ_ONCE(*ic); 238 236 } 239 237 new = old; 240 238 new.k = 1; ··· 251 253 goto out; 252 254 ic = &vcpu->kvm->arch.sca->ipte_control; 253 255 do { 254 - old = *ic; 255 - barrier(); 256 + old = READ_ONCE(*ic); 256 257 new = old; 257 258 new.k = 0; 258 259 } while (cmpxchg(&ic->val, old.val, new.val) != old.val); ··· 266 269 267 270 ic = &vcpu->kvm->arch.sca->ipte_control; 268 271 do { 269 - old = *ic; 270 - barrier(); 272 + old = READ_ONCE(*ic); 271 273 while (old.kg) { 272 274 cond_resched(); 273 - old = *ic; 274 - barrier(); 275 + old = READ_ONCE(*ic); 275 276 } 276 277 new = old; 277 278 new.k = 1; ··· 283 288 284 289 ic = &vcpu->kvm->arch.sca->ipte_control; 285 290 do { 286 - old = *ic; 287 - barrier(); 291 + old = READ_ONCE(*ic); 288 292 new = old; 289 293 new.kh--; 290 294 if (!new.kh)