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authorDenis Plotnikov <dplotnikov@virtuozzo.com>2017-04-07 05:09:52 -0400
committerRadim Krčmář <rkrcmar@redhat.com>2017-04-12 14:17:15 -0400
commitc5e8ec8e9beffb9481dba27ab5048c03c8585d7d (patch)
tree05586fdc5b1af75fd56476339aff0c12f3345aa7
parent900ab14ca93dce3f95fdb2bd9c4b654d4d5f2571 (diff)
KVM: x86: remaster kvm_write_tsc code
Reuse existing code instead of using inline asm. Make the code more concise and clear in the TSC synchronization part. Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com> Reviewed-by: Roman Kagan <rkagan@virtuozzo.com> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
-rw-r--r--arch/x86/kvm/x86.c52
1 files changed, 13 insertions, 39 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 3046b7f278ae..422f803fa365 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1443,10 +1443,10 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, struct msr_data *msr)
1443 struct kvm *kvm = vcpu->kvm; 1443 struct kvm *kvm = vcpu->kvm;
1444 u64 offset, ns, elapsed; 1444 u64 offset, ns, elapsed;
1445 unsigned long flags; 1445 unsigned long flags;
1446 s64 usdiff;
1447 bool matched; 1446 bool matched;
1448 bool already_matched; 1447 bool already_matched;
1449 u64 data = msr->data; 1448 u64 data = msr->data;
1449 bool synchronizing = false;
1450 1450
1451 raw_spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags); 1451 raw_spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags);
1452 offset = kvm_compute_tsc_offset(vcpu, data); 1452 offset = kvm_compute_tsc_offset(vcpu, data);
@@ -1454,51 +1454,25 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, struct msr_data *msr)
1454 elapsed = ns - kvm->arch.last_tsc_nsec; 1454 elapsed = ns - kvm->arch.last_tsc_nsec;
1455 1455
1456 if (vcpu->arch.virtual_tsc_khz) { 1456 if (vcpu->arch.virtual_tsc_khz) {
1457 int faulted = 0; 1457 u64 tsc_exp = kvm->arch.last_tsc_write +
1458 1458 nsec_to_cycles(vcpu, elapsed);
1459 /* n.b - signed multiplication and division required */ 1459 u64 tsc_hz = vcpu->arch.virtual_tsc_khz * 1000LL;
1460 usdiff = data - kvm->arch.last_tsc_write; 1460 /*
1461#ifdef CONFIG_X86_64 1461 * Special case: TSC write with a small delta (1 second)
1462 usdiff = (usdiff * 1000) / vcpu->arch.virtual_tsc_khz; 1462 * of virtual cycle time against real time is
1463#else 1463 * interpreted as an attempt to synchronize the CPU.
1464 /* do_div() only does unsigned */ 1464 */
1465 asm("1: idivl %[divisor]\n" 1465 synchronizing = data < tsc_exp + tsc_hz &&
1466 "2: xor %%edx, %%edx\n" 1466 data + tsc_hz > tsc_exp;
1467 " movl $0, %[faulted]\n" 1467 }
1468 "3:\n"
1469 ".section .fixup,\"ax\"\n"
1470 "4: movl $1, %[faulted]\n"
1471 " jmp 3b\n"
1472 ".previous\n"
1473
1474 _ASM_EXTABLE(1b, 4b)
1475
1476 : "=A"(usdiff), [faulted] "=r" (faulted)
1477 : "A"(usdiff * 1000), [divisor] "rm"(vcpu->arch.virtual_tsc_khz));
1478
1479#endif
1480 do_div(elapsed, 1000);
1481 usdiff -= elapsed;
1482 if (usdiff < 0)
1483 usdiff = -usdiff;
1484
1485 /* idivl overflow => difference is larger than USEC_PER_SEC */
1486 if (faulted)
1487 usdiff = USEC_PER_SEC;
1488 } else
1489 usdiff = USEC_PER_SEC; /* disable TSC match window below */
1490 1468
1491 /* 1469 /*
1492 * Special case: TSC write with a small delta (1 second) of virtual
1493 * cycle time against real time is interpreted as an attempt to
1494 * synchronize the CPU.
1495 *
1496 * For a reliable TSC, we can match TSC offsets, and for an unstable 1470 * For a reliable TSC, we can match TSC offsets, and for an unstable
1497 * TSC, we add elapsed time in this computation. We could let the 1471 * TSC, we add elapsed time in this computation. We could let the
1498 * compensation code attempt to catch up if we fall behind, but 1472 * compensation code attempt to catch up if we fall behind, but
1499 * it's better to try to match offsets from the beginning. 1473 * it's better to try to match offsets from the beginning.
1500 */ 1474 */
1501 if (usdiff < USEC_PER_SEC && 1475 if (synchronizing &&
1502 vcpu->arch.virtual_tsc_khz == kvm->arch.last_tsc_khz) { 1476 vcpu->arch.virtual_tsc_khz == kvm->arch.last_tsc_khz) {
1503 if (!check_tsc_unstable()) { 1477 if (!check_tsc_unstable()) {
1504 offset = kvm->arch.cur_tsc_offset; 1478 offset = kvm->arch.cur_tsc_offset;