From: Xiong Zhang <[email protected]>
In PMU passthrough mode, use global_ctrl field in struct kvm_pmu as the
cached value. This is convenient for KVM to set and get the value from the
host side. In addition, load and save the value across VM enter/exit
boundary in the following way:
- At VM exit, if processor supports
GUEST_VM_EXIT_SAVE_IA32_PERF_GLOBAL_CTRL, read guest
IA32_PERF_GLOBAL_CTRL GUEST_IA32_PERF_GLOBAL_CTRL VMCS field, else read
it from VM-exit MSR-stroe array in VMCS. The value is then assigned to
global_ctrl.
- At VM Entry, if processor supports
GUEST_VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL, read guest
IA32_PERF_GLOBAL_CTRL from GUEST_IA32_PERF_GLOBAL_CTRL VMCS field, else
read it from VM-entry MSR-load array in VMCS. The value is then
assigned to global ctrl.
Implement the above logic into two helper functions and invoke them around
VM Enter/exit boundary.
Co-developed-by: Mingwei Zhang <[email protected]>
Signed-off-by: Mingwei Zhang <[email protected]>
Signed-off-by: Xiong Zhang <[email protected]>
---
arch/x86/kvm/vmx/vmx.c | 51 +++++++++++++++++++++++++++++++++++++++++-
1 file changed, 50 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 50100954cd92..a9623351eafe 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7193,7 +7193,7 @@ static void vmx_cancel_injection(struct kvm_vcpu *vcpu)
vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, 0);
}
-static void atomic_switch_perf_msrs(struct vcpu_vmx *vmx)
+static void __atomic_switch_perf_msrs(struct vcpu_vmx *vmx)
{
int i, nr_msrs;
struct perf_guest_switch_msr *msrs;
@@ -7216,6 +7216,52 @@ static void atomic_switch_perf_msrs(struct vcpu_vmx *vmx)
msrs[i].host, false);
}
+static void save_perf_global_ctrl_in_passthrough_pmu(struct vcpu_vmx *vmx)
+{
+ struct kvm_pmu *pmu = vcpu_to_pmu(&vmx->vcpu);
+ int i;
+
+ if (vm_exit_controls_get(vmx) & VM_EXIT_SAVE_IA32_PERF_GLOBAL_CTRL) {
+ pmu->global_ctrl = vmcs_read64(GUEST_IA32_PERF_GLOBAL_CTRL);
+ } else {
+ i = vmx_find_loadstore_msr_slot(&vmx->msr_autostore.guest,
+ MSR_CORE_PERF_GLOBAL_CTRL);
+ if (i < 0)
+ return;
+ pmu->global_ctrl = vmx->msr_autostore.guest.val[i].value;
+ }
+}
+
+static void load_perf_global_ctrl_in_passthrough_pmu(struct vcpu_vmx *vmx)
+{
+ u64 global_ctrl = vcpu_to_pmu(&vmx->vcpu)->global_ctrl;
+ int i;
+
+ if (vm_entry_controls_get(vmx) & VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL) {
+ vmcs_write64(GUEST_IA32_PERF_GLOBAL_CTRL, global_ctrl);
+ } else {
+ i = vmx_find_loadstore_msr_slot(&vmx->msr_autoload.guest,
+ MSR_CORE_PERF_GLOBAL_CTRL);
+ if (i < 0)
+ return;
+
+ vmx->msr_autoload.guest.val[i].value = global_ctrl;
+ }
+}
+
+static void __atomic_switch_perf_msrs_in_passthrough_pmu(struct vcpu_vmx *vmx)
+{
+ load_perf_global_ctrl_in_passthrough_pmu(vmx);
+}
+
+static void atomic_switch_perf_msrs(struct vcpu_vmx *vmx)
+{
+ if (is_passthrough_pmu_enabled(&vmx->vcpu))
+ __atomic_switch_perf_msrs_in_passthrough_pmu(vmx);
+ else
+ __atomic_switch_perf_msrs(vmx);
+}
+
static void vmx_update_hv_timer(struct kvm_vcpu *vcpu)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
@@ -7314,6 +7360,9 @@ static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu,
vcpu->arch.cr2 = native_read_cr2();
vcpu->arch.regs_avail &= ~VMX_REGS_LAZY_LOAD_SET;
+ if (is_passthrough_pmu_enabled(vcpu))
+ save_perf_global_ctrl_in_passthrough_pmu(vmx);
+
vmx->idt_vectoring_info = 0;
vmx_enable_fb_clear(vmx);
--
2.34.1
On Fri, Jan 26, 2024, Xiong Zhang wrote:
> +static void save_perf_global_ctrl_in_passthrough_pmu(struct vcpu_vmx *vmx)
> +{
> + struct kvm_pmu *pmu = vcpu_to_pmu(&vmx->vcpu);
> + int i;
> +
> + if (vm_exit_controls_get(vmx) & VM_EXIT_SAVE_IA32_PERF_GLOBAL_CTRL) {
> + pmu->global_ctrl = vmcs_read64(GUEST_IA32_PERF_GLOBAL_CTRL);
> + } else {
> + i = vmx_find_loadstore_msr_slot(&vmx->msr_autostore.guest,
> + MSR_CORE_PERF_GLOBAL_CTRL);
> + if (i < 0)
> + return;
> + pmu->global_ctrl = vmx->msr_autostore.guest.val[i].value;
As before, NAK to using the MSR load/store lists unless there's a *really* good
reason I'm missing.
And we should consider adding VCPU_EXREG_GLOBAL_CTRL so that we can defer the
VMREAD until KVM actually tries to access the guest value.
On Thu, Apr 11, 2024 at 2:54 PM Sean Christopherson <[email protected]> wrote:
>
> On Fri, Jan 26, 2024, Xiong Zhang wrote:
> > +static void save_perf_global_ctrl_in_passthrough_pmu(struct vcpu_vmx *vmx)
> > +{
> > + struct kvm_pmu *pmu = vcpu_to_pmu(&vmx->vcpu);
> > + int i;
> > +
> > + if (vm_exit_controls_get(vmx) & VM_EXIT_SAVE_IA32_PERF_GLOBAL_CTRL) {
> > + pmu->global_ctrl = vmcs_read64(GUEST_IA32_PERF_GLOBAL_CTRL);
> > + } else {
> > + i = vmx_find_loadstore_msr_slot(&vmx->msr_autostore.guest,
> > + MSR_CORE_PERF_GLOBAL_CTRL);
> > + if (i < 0)
> > + return;
> > + pmu->global_ctrl = vmx->msr_autostore.guest.val[i].value;
>
> As before, NAK to using the MSR load/store lists unless there's a *really* good
> reason I'm missing.
The VM-exit control, "save IA32_PERF_GLOBAL_CTL," first appears in
Sapphire Rapids. I think that's a compelling reason.
> And we should consider adding VCPU_EXREG_GLOBAL_CTRL so that we can defer the
> VMREAD until KVM actually tries to access the guest value.
On Thu, Apr 11, 2024, Jim Mattson wrote:
> On Thu, Apr 11, 2024 at 2:54 PM Sean Christopherson <[email protected]> wrote:
> >
> > On Fri, Jan 26, 2024, Xiong Zhang wrote:
> > > +static void save_perf_global_ctrl_in_passthrough_pmu(struct vcpu_vmx *vmx)
> > > +{
> > > + struct kvm_pmu *pmu = vcpu_to_pmu(&vmx->vcpu);
> > > + int i;
> > > +
> > > + if (vm_exit_controls_get(vmx) & VM_EXIT_SAVE_IA32_PERF_GLOBAL_CTRL) {
> > > + pmu->global_ctrl = vmcs_read64(GUEST_IA32_PERF_GLOBAL_CTRL);
> > > + } else {
> > > + i = vmx_find_loadstore_msr_slot(&vmx->msr_autostore.guest,
> > > + MSR_CORE_PERF_GLOBAL_CTRL);
> > > + if (i < 0)
> > > + return;
> > > + pmu->global_ctrl = vmx->msr_autostore.guest.val[i].value;
> >
> > As before, NAK to using the MSR load/store lists unless there's a *really* good
> > reason I'm missing.
>
> The VM-exit control, "save IA32_PERF_GLOBAL_CTL," first appears in
> Sapphire Rapids. I think that's a compelling reason.
Well that's annoying. When was PMU v4 introduced? E.g. if it came in ICX, I'd
be sorely tempted to make VM_EXIT_SAVE_IA32_PERF_GLOBAL_CTRL a hard requirement.
And has someone confirmed that the CPU saves into the MSR store list before
processing VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL?
Assuming we don't make VM_EXIT_SAVE_IA32_PERF_GLOBAL_CTRL a hard requirement,
this code should be cleaned up and simplified. It should be impossible to get
to this point with a passthrough PMU and no slot for saving guest GLOBAL_CTRL.
E.g. this could simply be:
if (cpu_has_save_perf_global_ctrl())
pmu->global_ctrl = vmcs_read64(GUEST_IA32_PERF_GLOBAL_CTRL);
else
pmu->global_ctrl = *pmu->__global_ctrl;
where vmx_set_perf_global_ctrl() sets __global_ctrl to:
pmu->__global_ctrl = &vmx->msr_autostore.guest.val[i].value;
KVM could store 'i', i.e. the slot, but in the end it's 4 bytes per vCPU (assuming
64-bit kernel, and an int to store the slot).
Oh, by the by, vmx_set_perf_global_ctrl() is buggy, as it neglects to *remove*
PERF_GLOBAL_CTRL from the lists if userspace sets CPUID multiple times.