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KVM: x86: remaster kvm_write_tsc code

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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>
This commit is contained in:
Denis Plotnikov 2017-04-07 12:09:52 +03:00 committed by Radim Krčmář
parent 900ab14ca9
commit c5e8ec8e9b
1 changed files with 13 additions and 39 deletions
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52
arch/x86/kvm/x86.c
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@ -1443,10 +1443,10 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, struct msr_data *msr)
struct kvm *kvm = vcpu->kvm;
u64 offset, ns, elapsed;
unsigned long flags;
s64 usdiff;
bool matched;
bool already_matched;
u64 data = msr->data;
bool synchronizing = false;
raw_spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags);
offset = kvm_compute_tsc_offset(vcpu, data);
@ -1454,51 +1454,25 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, struct msr_data *msr)
elapsed = ns - kvm->arch.last_tsc_nsec;
if (vcpu->arch.virtual_tsc_khz) {
int faulted = 0;
/* n.b - signed multiplication and division required */
usdiff = data - kvm->arch.last_tsc_write;
#ifdef CONFIG_X86_64
usdiff = (usdiff * 1000) / vcpu->arch.virtual_tsc_khz;
#else
/* do_div() only does unsigned */
asm("1: idivl %[divisor]\n"
"2: xor %%edx, %%edx\n"
" movl $0, %[faulted]\n"
"3:\n"
".section .fixup,\"ax\"\n"
"4: movl $1, %[faulted]\n"
" jmp 3b\n"
".previous\n"
_ASM_EXTABLE(1b, 4b)
: "=A"(usdiff), [faulted] "=r" (faulted)
: "A"(usdiff * 1000), [divisor] "rm"(vcpu->arch.virtual_tsc_khz));
#endif
do_div(elapsed, 1000);
usdiff -= elapsed;
if (usdiff < 0)
usdiff = -usdiff;
/* idivl overflow => difference is larger than USEC_PER_SEC */
if (faulted)
usdiff = USEC_PER_SEC;
} else
usdiff = USEC_PER_SEC; /* disable TSC match window below */
u64 tsc_exp = kvm->arch.last_tsc_write +
nsec_to_cycles(vcpu, elapsed);
u64 tsc_hz = vcpu->arch.virtual_tsc_khz * 1000LL;
/*
* Special case: TSC write with a small delta (1 second)
* of virtual cycle time against real time is
* interpreted as an attempt to synchronize the CPU.
*/
synchronizing = data < tsc_exp + tsc_hz &&
data + tsc_hz > tsc_exp;
}
/*
* Special case: TSC write with a small delta (1 second) of virtual
* cycle time against real time is interpreted as an attempt to
* synchronize the CPU.
*
* For a reliable TSC, we can match TSC offsets, and for an unstable
* TSC, we add elapsed time in this computation. We could let the
* compensation code attempt to catch up if we fall behind, but
* it's better to try to match offsets from the beginning.
*/
if (usdiff < USEC_PER_SEC &&
if (synchronizing &&
vcpu->arch.virtual_tsc_khz == kvm->arch.last_tsc_khz) {
if (!check_tsc_unstable()) {
offset = kvm->arch.cur_tsc_offset;