2016-07-28 06:30-0700, Jim Mattson:
> I'm going to be on vacation next week, but I'll address these concerns
> when I return. If time permits, I'll send out a patch this week that
> just addresses the issue of doing a VMPTRLD before putting the VMCS on
> the loaded VMCSs list.
Ah, I missed the point of that hunk. It is not related to nVMX so
fixing it in a separate patch would be best.
Thanks.
> On Wed, Jul 27, 2016 at 2:53 PM, Bandan Das <bsd@xxxxxxxxxx> wrote:
>> Radim Krčmář <rkrcmar@xxxxxxxxxx> writes:
>>
>>> 2016-07-22 11:25-0700, Jim Mattson:
>>>> If a shadow VMCS is referenced by the VMCS link pointer in the
>>>> current VMCS, then VM-entry makes the shadow VMCS active on the
>>>> current processor. No VMCS should ever be active on more than one
>>>> processor. If a VMCS is to be migrated from one processor to
>>>> another, software should execute a VMCLEAR for the VMCS on the
>>>> first processor before the VMCS is made active on the second
>>>> processor.
>>>>
>>>> We already keep track of ordinary VMCSs that are made active by
>>>> VMPTRLD. Extend that tracking to handle shadow VMCSs that are
>>>> made active by VM-entry to their parents.
>>>>
>>>> Signed-off-by: Jim Mattson <jmattson@xxxxxxxxxx>
>>>> ---
>>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>>>> @@ -2113,6 +2113,15 @@ static void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu)
>>>> new.control) != old.control);
>>>> }
>>>>
>>>> +static void record_loaded_vmcs(struct loaded_vmcs *loaded_vmcs, int cpu)
>>>> +{
>>>> + if (loaded_vmcs->vmcs) {
>>>> + list_add(&loaded_vmcs->loaded_vmcss_on_cpu_link,
>>>> + &per_cpu(loaded_vmcss_on_cpu, cpu));
>>>> + loaded_vmcs->cpu = cpu;
>>>> + }
>>>> +}
>>>> +
>>>> /*
>>>> * Switches to specified vcpu, until a matching vcpu_put(), but assumes
>>>> * vcpu mutex is already taken.
>>>> @@ -2124,15 +2133,13 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>>>>
>>>> if (!vmm_exclusive)
>>>> kvm_cpu_vmxon(phys_addr);
>>>> - else if (vmx->loaded_vmcs->cpu != cpu)
>>>> + else if (vmx->loaded_vmcs->cpu != cpu) {
>>>> loaded_vmcs_clear(vmx->loaded_vmcs);
>>>> + if (vmx->nested.current_shadow_vmcs.vmcs)
>>>> + loaded_vmcs_clear(&vmx->nested.current_shadow_vmcs);
>>>
>>> loaded_vmcs_clear() uses expensive IPI, so would want to do both in one
>>> call in future patches as they are always active on the same CPU.
>>
>> Maybe just move the check for an active shadow vmcs to loaded_vmcs_clear
>> and clear it there unconditionally.
>>
>>> Another possible complication is marking current_shadow_vmcs as active
>>> on a cpu only after a successful vmlaunch.
>>> (We don't seem to ever vmptrld shadow vmcs explicitly.)
>>>
>>>> + }
>>>
>>> Incorrect whitespace for indentation.
>>>
>>>>
>>>> if (per_cpu(current_vmcs, cpu) != vmx->loaded_vmcs->vmcs) {
>>>> - per_cpu(current_vmcs, cpu) = vmx->loaded_vmcs->vmcs;
>>>> - vmcs_load(vmx->loaded_vmcs->vmcs);
>>>> - }
>>>> -
>>>> - if (vmx->loaded_vmcs->cpu != cpu) {
>>>
>>> This condition is nice for performance because a non-current vmcs is
>>> usually already active on the same CPU, so we skip all the code below.
>>>
>>> (This is the only thing that has to be fixed as it regresses non-nested,
>>> the rest are mostly ideas for simplifications.)
>>
>> I think he wanted to make sure to call vmcs_load after the call
>> to crash_disable_local_vmclear() but that should be possible without
>> removing the check.
>>
>> Bandan
>>
>>>> struct desc_ptr *gdt = this_cpu_ptr(&host_gdt);
>>>> unsigned long sysenter_esp;
>>>>
>>>> @@ -2147,11 +2154,15 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>>>> */
>>>> smp_rmb();
>>>>
>>>> - list_add(&vmx->loaded_vmcs->loaded_vmcss_on_cpu_link,
>>>> - &per_cpu(loaded_vmcss_on_cpu, cpu));
>>>> + record_loaded_vmcs(vmx->loaded_vmcs, cpu);
>>>
>>> Adding and an element to a list multiple times seems invalid, which the
>>> condition was also guarding.
>>>
>>>> + record_loaded_vmcs(&vmx->nested.current_shadow_vmcs, cpu);
>>>
>>> current_shadow_vmcs is always active on the same cpu as loaded_vmcs ...
>>> I think we could skip the list and just clear current_shadow_vmcs when
>>> clearing its loaded_vmcs.
>>>
>>>> crash_enable_local_vmclear(cpu);
>>>> local_irq_enable();
>>>>
>>>> + per_cpu(current_vmcs, cpu) = vmx->loaded_vmcs->vmcs;
>>>> + vmcs_load(vmx->loaded_vmcs->vmcs);
>>>> +
>>>> /*
>>>> * Linux uses per-cpu TSS and GDT, so set these when switching
>>>> * processors.
>>>> @@ -2161,8 +2172,6 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>>>>
>>>> rdmsrl(MSR_IA32_SYSENTER_ESP, sysenter_esp);
>>>> vmcs_writel(HOST_IA32_SYSENTER_ESP, sysenter_esp); /* 22.2.3 */
>>>> -
>>>> - vmx->loaded_vmcs->cpu = cpu;
>>>> }
>>>>
>>>> /* Setup TSC multiplier */
>>>> @@ -6812,6 +6821,34 @@ static int nested_vmx_check_vmptr(struct kvm_vcpu *vcpu, int exit_reason,
>>>> return 0;
>>>> }
>>>>
>>>> +static int setup_shadow_vmcs(struct vcpu_vmx *vmx)
>>>> +{
>>>> + struct vmcs *shadow_vmcs;
>>>> + int cpu;
>>>> +
>>>> + shadow_vmcs = alloc_vmcs();
>>>> + if (!shadow_vmcs)
>>>> + return -ENOMEM;
>>>> +
>>>> + /* mark vmcs as shadow */
>>>> + shadow_vmcs->revision_id |= (1u << 31);
>>>> + /* init shadow vmcs */
>>>> + vmx->nested.current_shadow_vmcs.vmcs = shadow_vmcs;
>>>> + loaded_vmcs_init(&vmx->nested.current_shadow_vmcs);
>>>> +
>>>> + cpu = get_cpu();
>>>> + local_irq_disable();
>>>> + crash_disable_local_vmclear(cpu);
>>>> +
>>>> + record_loaded_vmcs(&vmx->nested.current_shadow_vmcs, cpu);
>>>
>>> This could be avoided if we assumed that shadow vmcs is always active on
>>> the same vcpu. The assumption looks rock-solid, because shadow vmcs is
>>> activated on vmlaunch and its linking vmcs must be active (and current)
>>> on the same CPU.
>>>
>>>> +
>>>> + crash_enable_local_vmclear(cpu);
>>>> + local_irq_enable();
>>>> + put_cpu();
>>>> +
>>>> + return 0;
>>>> +}
>>>> +
>>>> /*
>>>> * Emulate the VMXON instruction.
>>>> * Currently, we just remember that VMX is active, and do not save or even
>>>> @@ -6867,14 +6903,9 @@ static int handle_vmon(struct kvm_vcpu *vcpu)
>>>> }
>>>>
>>>> if (enable_shadow_vmcs) {
>>>> - shadow_vmcs = alloc_vmcs();
>>>> - if (!shadow_vmcs)
>>>> - return -ENOMEM;
>>>> - /* mark vmcs as shadow */
>>>> - shadow_vmcs->revision_id |= (1u << 31);
>>>> - /* init shadow vmcs */
>>>> - vmcs_clear(shadow_vmcs);
>>>> - vmx->nested.current_shadow_vmcs = shadow_vmcs;
>>>> + int ret = setup_shadow_vmcs(vmx);
>>>> + if (ret < 0)
>>>> + return ret;
>>>> }
>>>>
>>>> INIT_LIST_HEAD(&(vmx->nested.vmcs02_pool));
--
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