git: a7db532e3a6f - main - vmm: Simplify saving of absolute TSC values in snapshots.
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Date: Fri, 18 Nov 2022 18:26:21 UTC
The branch main has been updated by jhb: URL: https://cgit.FreeBSD.org/src/commit/?id=a7db532e3a6f83067b342f569b56076d011f8a1e commit a7db532e3a6f83067b342f569b56076d011f8a1e Author: John Baldwin <jhb@FreeBSD.org> AuthorDate: 2022-11-18 17:57:29 +0000 Commit: John Baldwin <jhb@FreeBSD.org> CommitDate: 2022-11-18 18:25:34 +0000 vmm: Simplify saving of absolute TSC values in snapshots. 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 --- sys/amd64/vmm/vmm.c | 35 ++++++++--------------------------- 1 file changed, 8 insertions(+), 27 deletions(-) diff --git a/sys/amd64/vmm/vmm.c b/sys/amd64/vmm/vmm.c index dc6e03303b44..124fffec0d9e 100644 --- a/sys/amd64/vmm/vmm.c +++ b/sys/amd64/vmm/vmm.c @@ -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);