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vmm: Simplify saving of absolute TSC values in snapshots.

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Read the current "now" TSC value and use it to compute absolute time
saved value in vm_snapshot_vcpus rather than iterating over vCPUs
multiple times in vm_snapshot_vm.

Reviewed by:	corvink, markj
Differential Revision:	https://reviews.freebsd.org/D37146
This commit is contained in:
John Baldwin 2022-11-18 09:57:29 -08:00
parent 1e9c9ab595
commit a7db532e3a
1 changed files with 8 additions and 27 deletions
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35
sys/amd64/vmm/vmm.c
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@ -2804,10 +2804,12 @@ VMM_STAT_FUNC(VMM_MEM_WIRED, "Wired memory", vm_get_wiredcnt);
static int
vm_snapshot_vcpus(struct vm *vm, struct vm_snapshot_meta *meta)
{
uint64_t tsc, now;
int ret;
int i;
struct vcpu *vcpu;
now = rdtsc();
for (i = 0; i < VM_MAXCPU; i++) {
vcpu = &vm->vcpu[i];
@ -2819,13 +2821,15 @@ vm_snapshot_vcpus(struct vm *vm, struct vm_snapshot_meta *meta)
SNAPSHOT_VAR_OR_LEAVE(vcpu->guest_xcr0, meta, ret, done);
SNAPSHOT_VAR_OR_LEAVE(vcpu->exitinfo, meta, ret, done);
SNAPSHOT_VAR_OR_LEAVE(vcpu->nextrip, meta, ret, done);
/* XXX we're cheating here, since the value of tsc_offset as
* saved here is actually the value of the guest's TSC value.
/*
* Save the absolute TSC value by adding now to tsc_offset.
*
* It will be turned turned back into an actual offset when the
* TSC restore function is called
*/
SNAPSHOT_VAR_OR_LEAVE(vcpu->tsc_offset, meta, ret, done);
tsc = now + vcpu->tsc_offset;
SNAPSHOT_VAR_OR_LEAVE(tsc, meta, ret, done);
}
done:
@ -2836,33 +2840,10 @@ static int
vm_snapshot_vm(struct vm *vm, struct vm_snapshot_meta *meta)
{
int ret;
int i;
uint64_t now;
ret = 0;
now = rdtsc();
if (meta->op == VM_SNAPSHOT_SAVE) {
/* XXX make tsc_offset take the value TSC proper as seen by the
* guest
*/
for (i = 0; i < VM_MAXCPU; i++)
vm->vcpu[i].tsc_offset += now;
}
ret = vm_snapshot_vcpus(vm, meta);
if (ret != 0) {
printf("%s: failed to copy vm data to user buffer", __func__);
if (ret != 0)
goto done;
}
if (meta->op == VM_SNAPSHOT_SAVE) {
/* XXX turn tsc_offset back into an offset; actual value is only
* required for restore; using it otherwise would be wrong
*/
for (i = 0; i < VM_MAXCPU; i++)
vm->vcpu[i].tsc_offset -= now;
}
done:
return (ret);