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

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Message-ID: <c354709d-6774-8ad5-7cc9-dbfb789ba0d2@gmail.com>
Date:   Mon, 11 Dec 2017 13:15:35 +0800
From:   Quan Xu <quan.xu0@...il.com>
To:     David Hildenbrand <david@...hat.com>, kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, rkrcmar@...hat.com,
        jmattson@...gle.com, pbonzini@...hat.com
Subject: Re: [PATCH] KVM: VMX: drop I/O permission bitmaps



On 2017/12/09 00:18, David Hildenbrand wrote:
> On 08.12.2017 11:22, Quan Xu wrote:
>> From: Quan Xu <quan.xu0@...il.com>
>>
>> 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@...gle.com>
>> Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
>> Signed-off-by: Quan Xu <quan.xu0@...il.com>
>> ---
>>   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