Re: [PATCH] KVM: VMX: drop I/O permission bitmaps

[Quan Xu <quan.xu0@xxxxxxxxx>]

On 2017/12/09 00:18, David Hildenbrand wrote:
> On 08.12.2017 11:22, Quan Xu wrote:
> > From: Quan Xu <quan.xu0@xxxxxxxxx>
> >
> > Since KVM removes the only I/O port 0x80 bypass on Intel hosts,
> > clear CPU_BASED_USE_IO_BITMAPS and set CPU_BASED_UNCOND_IO_EXITING
> > bit. Then these I/O permission bitmaps are not used at all, so
> > drop I/O permission bitmaps.
> >
> > Signed-off-by: Jim Mattson <jmattson@xxxxxxxxxx>
> > Signed-off-by: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> > Signed-off-by: Quan Xu <quan.xu0@xxxxxxxxx>
> > ---
> >   arch/x86/kvm/vmx.c |   17 +----------------
> >   1 files changed, 1 insertions(+), 16 deletions(-)
> >
> > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> > index 2fd9a8c..3e4f760 100644
> > --- a/arch/x86/kvm/vmx.c
> > +++ b/arch/x86/kvm/vmx.c
> > @@ -771,8 +771,6 @@ enum segment_cache_field {
> >   	FIELD(HOST_FS_SELECTOR, host_fs_selector),
> >   	FIELD(HOST_GS_SELECTOR, host_gs_selector),
> >   	FIELD(HOST_TR_SELECTOR, host_tr_selector),
> > -	FIELD64(IO_BITMAP_A, io_bitmap_a),
> > -	FIELD64(IO_BITMAP_B, io_bitmap_b),
> >   	FIELD64(MSR_BITMAP, msr_bitmap),
> >   	FIELD64(VM_EXIT_MSR_STORE_ADDR, vm_exit_msr_store_addr),
> >   	FIELD64(VM_EXIT_MSR_LOAD_ADDR, vm_exit_msr_load_addr),
> > @@ -943,8 +941,6 @@ static bool nested_vmx_is_page_fault_vmexit(struct vmcs12 *vmcs12,
> >   static DEFINE_PER_CPU(spinlock_t, blocked_vcpu_on_cpu_lock);
> >   
> >   enum {
> > -	VMX_IO_BITMAP_A,
> > -	VMX_IO_BITMAP_B,
> >   	VMX_MSR_BITMAP_LEGACY,
> >   	VMX_MSR_BITMAP_LONGMODE,
> >   	VMX_MSR_BITMAP_LEGACY_X2APIC_APICV,
> > @@ -958,8 +954,6 @@ enum {
> >   
> >   static unsigned long *vmx_bitmap[VMX_BITMAP_NR];
> >   
> > -#define vmx_io_bitmap_a                      (vmx_bitmap[VMX_IO_BITMAP_A])
> > -#define vmx_io_bitmap_b                      (vmx_bitmap[VMX_IO_BITMAP_B])
> >   #define vmx_msr_bitmap_legacy                (vmx_bitmap[VMX_MSR_BITMAP_LEGACY])
> >   #define vmx_msr_bitmap_longmode              (vmx_bitmap[VMX_MSR_BITMAP_LONGMODE])
> >   #define vmx_msr_bitmap_legacy_x2apic_apicv   (vmx_bitmap[VMX_MSR_BITMAP_LEGACY_X2APIC_APICV])
> > @@ -3632,7 +3626,7 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf)
> >   #endif
> >   	      CPU_BASED_CR3_LOAD_EXITING |
> >   	      CPU_BASED_CR3_STORE_EXITING |
> > -	      CPU_BASED_USE_IO_BITMAPS |
> > +	      CPU_BASED_UNCOND_IO_EXITING |
> >   	      CPU_BASED_MOV_DR_EXITING |
> >   	      CPU_BASED_USE_TSC_OFFSETING |
> >   	      CPU_BASED_INVLPG_EXITING |
> > @@ -5445,10 +5439,6 @@ static void vmx_vcpu_setup(struct vcpu_vmx *vmx)
> >   #endif
> >   	int i;
> >   
> > -	/* I/O */
> > -	vmcs_write64(IO_BITMAP_A, __pa(vmx_io_bitmap_a));
> > -	vmcs_write64(IO_BITMAP_B, __pa(vmx_io_bitmap_b));
> > -
> >   	if (enable_shadow_vmcs) {
> >   		vmcs_write64(VMREAD_BITMAP, __pa(vmx_vmread_bitmap));
> >   		vmcs_write64(VMWRITE_BITMAP, __pa(vmx_vmwrite_bitmap));
> > @@ -6751,14 +6741,9 @@ static __init int hardware_setup(void)
> >   			goto out;
> >   	}
> >   
> > -	vmx_io_bitmap_b = (unsigned long *)__get_free_page(GFP_KERNEL);
> >   	memset(vmx_vmread_bitmap, 0xff, PAGE_SIZE);
> >   	memset(vmx_vmwrite_bitmap, 0xff, PAGE_SIZE);
> >   
> > -	memset(vmx_io_bitmap_a, 0xff, PAGE_SIZE);
> > -
> > -	memset(vmx_io_bitmap_b, 0xff, PAGE_SIZE);
> > -
> >   	memset(vmx_msr_bitmap_legacy, 0xff, PAGE_SIZE);
> >   	memset(vmx_msr_bitmap_longmode, 0xff, PAGE_SIZE);
> >   
> Looks good to me.

David, thanks for your review.

> We could now also drop
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index a5d2856eb28b..732e93332f4c 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -10639,7 +10639,6 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu,
> struct vmcs12 *vmcs12,
>           * Rather, exit every time.
>           */
>          exec_control &= ~CPU_BASED_USE_IO_BITMAPS;
> -       exec_control |= CPU_BASED_UNCOND_IO_EXITING;
>
>          vmcs_write32(CPU_BASED_VM_EXEC_CONTROL, exec_control);
>
> As this will be implicitly set by vmx_exec_control()

good catch.
yes, L0 merge vmcs01 with vmcsl2 to create vmcs02 and run L2.

however as this code is related to nested virtualization, I better 
introduce it in another new patch
with "KVM: NVMX" prefix subject after this patch is applied.

furthermore, I think I could drop these tow lines in another new patch:

-       exec_control &= ~CPU_BASED_USE_IO_BITMAPS;
-       exec_control |= CPU_BASED_UNCOND_IO_EXITING;

as the CPU_BASED_USE_IO_BITMAPS is clear after this patch.


Quan