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SubjectRe: [PATCH RFC] KVM: VMX: drop vmm_exclusive module parameter
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On 14/03/2017 21:30, Radim Krčmář wrote:
> 2017-03-10 12:47+0100, David Hildenbrand:
>> vmm_exclusive=0 leads to KVM setting X86_CR4_VMXE always and calling
>> VMXON only when the vcpu is loaded. X86_CR4_VMXE is used as an
>> indication in cpu_emergency_vmxoff() (called on kdump) if VMXOFF has to be
>> called. This is obviously not the case if both are used independtly.
>> Calling VMXOFF without a previous VMXON will result in an exception.
>>
>> In addition, X86_CR4_VMXE is used as a mean to test if VMX is already in
>> use by another VMM in hardware_enable(). So there can't really be
>> co-existance. If the other VMM is prepared for co-existance and does a
>> similar check, only one VMM can exist. If the other VMM is not prepared
>> and blindly sets/clears X86_CR4_VMXE, we will get inconsistencies with
>> X86_CR4_VMXE.
>>
>> As we also had bug reports related to clearing of vmcs with vmm_exclusive=0
>> this seems to be pretty much untested. So let's better drop it.
>
> Totally,
>
> Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>

Radim,

are you putting this in kvm/queue for 4.12?

Thanks,

Paolo

>> While at it, directly move setting/clearing X86_CR4_VMXE into
>> kvm_cpu_vmxon/off.
>>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
>> ---
>> arch/x86/kvm/vmx.c | 38 +++++++-------------------------------
>> 1 file changed, 7 insertions(+), 31 deletions(-)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 283aa86..bbbfe12 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -84,9 +84,6 @@ module_param_named(eptad, enable_ept_ad_bits, bool, S_IRUGO);
>> static bool __read_mostly emulate_invalid_guest_state = true;
>> module_param(emulate_invalid_guest_state, bool, S_IRUGO);
>>
>> -static bool __read_mostly vmm_exclusive = 1;
>> -module_param(vmm_exclusive, bool, S_IRUGO);
>> -
>> static bool __read_mostly fasteoi = 1;
>> module_param(fasteoi, bool, S_IRUGO);
>>
>> @@ -914,8 +911,6 @@ static void nested_release_page_clean(struct page *page)
>>
>> static unsigned long nested_ept_get_cr3(struct kvm_vcpu *vcpu);
>> static u64 construct_eptp(unsigned long root_hpa);
>> -static void kvm_cpu_vmxon(u64 addr);
>> -static void kvm_cpu_vmxoff(void);
>> static bool vmx_xsaves_supported(void);
>> static int vmx_set_tss_addr(struct kvm *kvm, unsigned int addr);
>> static void vmx_set_segment(struct kvm_vcpu *vcpu,
>> @@ -2235,15 +2230,10 @@ static void decache_tsc_multiplier(struct vcpu_vmx *vmx)
>> static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>> {
>> struct vcpu_vmx *vmx = to_vmx(vcpu);
>> - u64 phys_addr = __pa(per_cpu(vmxarea, cpu));
>> bool already_loaded = vmx->loaded_vmcs->cpu == cpu;
>>
>> - if (!vmm_exclusive)
>> - kvm_cpu_vmxon(phys_addr);
>> - else if (!already_loaded)
>> - loaded_vmcs_clear(vmx->loaded_vmcs);
>> -
>> if (!already_loaded) {
>> + loaded_vmcs_clear(vmx->loaded_vmcs);
>> local_irq_disable();
>> crash_disable_local_vmclear(cpu);
>>
>> @@ -2321,11 +2311,6 @@ static void vmx_vcpu_put(struct kvm_vcpu *vcpu)
>> vmx_vcpu_pi_put(vcpu);
>>
>> __vmx_load_host_state(to_vmx(vcpu));
>> - if (!vmm_exclusive) {
>> - __loaded_vmcs_clear(to_vmx(vcpu)->loaded_vmcs);
>> - vcpu->cpu = -1;
>> - kvm_cpu_vmxoff();
>> - }
>> }
>>
>> static void vmx_decache_cr0_guest_bits(struct kvm_vcpu *vcpu);
>> @@ -3416,6 +3401,7 @@ static __init int vmx_disabled_by_bios(void)
>>
>> static void kvm_cpu_vmxon(u64 addr)
>> {
>> + cr4_set_bits(X86_CR4_VMXE);
>> intel_pt_handle_vmx(1);
>>
>> asm volatile (ASM_VMX_VMXON_RAX
>> @@ -3458,12 +3444,8 @@ static int hardware_enable(void)
>> /* enable and lock */
>> wrmsrl(MSR_IA32_FEATURE_CONTROL, old | test_bits);
>> }
>> - cr4_set_bits(X86_CR4_VMXE);
>> -
>> - if (vmm_exclusive) {
>> - kvm_cpu_vmxon(phys_addr);
>> - ept_sync_global();
>> - }
>> + kvm_cpu_vmxon(phys_addr);
>> + ept_sync_global();
>>
>> native_store_gdt(this_cpu_ptr(&host_gdt));
>>
>> @@ -3489,15 +3471,13 @@ static void kvm_cpu_vmxoff(void)
>> asm volatile (__ex(ASM_VMX_VMXOFF) : : : "cc");
>>
>> intel_pt_handle_vmx(0);
>> + cr4_clear_bits(X86_CR4_VMXE);
>> }
>>
>> static void hardware_disable(void)
>> {
>> - if (vmm_exclusive) {
>> - vmclear_local_loaded_vmcss();
>> - kvm_cpu_vmxoff();
>> - }
>> - cr4_clear_bits(X86_CR4_VMXE);
>> + vmclear_local_loaded_vmcss();
>> + kvm_cpu_vmxoff();
>> }
>>
>> static __init int adjust_vmx_controls(u32 ctl_min, u32 ctl_opt,
>> @@ -9228,11 +9208,7 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
>> vmx->loaded_vmcs->shadow_vmcs = NULL;
>> if (!vmx->loaded_vmcs->vmcs)
>> goto free_msrs;
>> - if (!vmm_exclusive)
>> - kvm_cpu_vmxon(__pa(per_cpu(vmxarea, raw_smp_processor_id())));
>> loaded_vmcs_init(vmx->loaded_vmcs);
>> - if (!vmm_exclusive)
>> - kvm_cpu_vmxoff();
>>
>> cpu = get_cpu();
>> vmx_vcpu_load(&vmx->vcpu, cpu);
>> --
>> 2.9.3
>>

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