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Date: Sat, 19 Oct 2019 09:28:40 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Sean Christopherson <sean.j.christopherson@...el.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>,
Radim Krčmář <rkrcmar@...hat.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] KVM: VMX: Some minor refactor of MSR bitmap
On 10/19/2019 1:27 AM, Sean Christopherson wrote:
> On Fri, Oct 18, 2019 at 05:37:23PM +0800, Xiaoyao Li wrote:
>> Move the MSR bitmap capability check from vmx_disable_intercept_for_msr()
>> and vmx_enable_intercept_for_msr(), so that we can do the check far
>> early before we really want to touch the bitmap.
>>
>> Also, we can move the common MSR not-intercept setup to where msr bitmap
>> is actually used.
>>
>> Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
>> ---
>> Changes in v2:
>> - Remove the check of cpu_has_vmx_msr_bitmap() from
>> vmx_{disable,enable}_intercept_for_msr (Krish)
>> ---
>> arch/x86/kvm/vmx/vmx.c | 65 +++++++++++++++++++++---------------------
>> 1 file changed, 33 insertions(+), 32 deletions(-)
>>
>> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
>> index b083316a598d..017689d0144e 100644
>> --- a/arch/x86/kvm/vmx/vmx.c
>> +++ b/arch/x86/kvm/vmx/vmx.c
>> @@ -343,8 +343,8 @@ module_param_cb(vmentry_l1d_flush, &vmentry_l1d_flush_ops, NULL, 0644);
>>
>> static bool guest_state_valid(struct kvm_vcpu *vcpu);
>> static u32 vmx_segment_access_rights(struct kvm_segment *var);
>> -static __always_inline void vmx_disable_intercept_for_msr(unsigned long *msr_bitmap,
>> - u32 msr, int type);
>> +static __always_inline void vmx_set_intercept_for_msr(unsigned long *msr_bitmap,
>> + u32 msr, int type, bool value);
>>
>> void vmx_vmexit(void);
>>
>> @@ -2000,9 +2000,9 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>> * in the merging. We update the vmcs01 here for L1 as well
>> * since it will end up touching the MSR anyway now.
>> */
>> - vmx_disable_intercept_for_msr(vmx->vmcs01.msr_bitmap,
>> - MSR_IA32_SPEC_CTRL,
>> - MSR_TYPE_RW);
>> + vmx_set_intercept_for_msr(vmx->vmcs01.msr_bitmap,
>> + MSR_IA32_SPEC_CTRL,
>> + MSR_TYPE_RW, false);
>
> IMO this is a net negative. The explicit "disable" is significantly more
> intuitive than "set" with a %false param, e.g. at a quick glance it would
> be easy to think this code is "setting", i.e. "enabling" interception.
>
How about renaming it to vmx_switch_intercept_for_msr()?
or just add the cpu_has_vmx_msr_bitmap() check outside because the check
is removed in vmx_disable_intercept_for_msr()
>> break;
>> case MSR_IA32_PRED_CMD:
>> if (!msr_info->host_initiated &&
>> @@ -2028,8 +2028,9 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>> * vmcs02.msr_bitmap here since it gets completely overwritten
>> * in the merging.
>> */
>> - vmx_disable_intercept_for_msr(vmx->vmcs01.msr_bitmap, MSR_IA32_PRED_CMD,
>> - MSR_TYPE_W);
>> + vmx_set_intercept_for_msr(vmx->vmcs01.msr_bitmap,
>> + MSR_IA32_PRED_CMD,
>> + MSR_TYPE_W, false);
>> break;
>> case MSR_IA32_CR_PAT:
>> if (!kvm_pat_valid(data))
>> @@ -3599,9 +3600,6 @@ static __always_inline void vmx_disable_intercept_for_msr(unsigned long *msr_bit
>> {
>> int f = sizeof(unsigned long);
>>
>> - if (!cpu_has_vmx_msr_bitmap())
>> - return;
>
> As above, I'd rather keep these here. Functionally it changes nothing on
> CPUs with an MSR bitmap. For old CPUs, it saves all of two uops in paths
> that aren't performance critical.
>
>> -
>> if (static_branch_unlikely(&enable_evmcs))
>> evmcs_touch_msr_bitmap();
>>
>> @@ -3637,9 +3635,6 @@ static __always_inline void vmx_enable_intercept_for_msr(unsigned long *msr_bitm
>> {
>> int f = sizeof(unsigned long);
>>
>> - if (!cpu_has_vmx_msr_bitmap())
>> - return;
>> -
>> if (static_branch_unlikely(&enable_evmcs))
>> evmcs_touch_msr_bitmap();
>>
>> @@ -3673,6 +3668,9 @@ static __always_inline void vmx_enable_intercept_for_msr(unsigned long *msr_bitm
>> static __always_inline void vmx_set_intercept_for_msr(unsigned long *msr_bitmap,
>> u32 msr, int type, bool value)
>> {
>> + if (!cpu_has_vmx_msr_bitmap())
>> + return;
>> +
>> if (value)
>> vmx_enable_intercept_for_msr(msr_bitmap, msr, type);
>> else
>> @@ -4163,11 +4161,30 @@ static void ept_set_mmio_spte_mask(void)
>>
>> static void vmx_vmcs_setup(struct vcpu_vmx *vmx)
>> {
>> + unsigned long *msr_bitmap;
>> +
>> if (nested)
>> nested_vmx_vmcs_setup();
>>
>> - if (cpu_has_vmx_msr_bitmap())
>> + if (cpu_has_vmx_msr_bitmap()) {
>> + msr_bitmap = vmx->vmcs01.msr_bitmap;
>> + vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_TSC, MSR_TYPE_R);
>> + vmx_disable_intercept_for_msr(msr_bitmap, MSR_FS_BASE, MSR_TYPE_RW);
>> + vmx_disable_intercept_for_msr(msr_bitmap, MSR_GS_BASE, MSR_TYPE_RW);
>> + vmx_disable_intercept_for_msr(msr_bitmap, MSR_KERNEL_GS_BASE, MSR_TYPE_RW);
>> + vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_SYSENTER_CS, MSR_TYPE_RW);
>> + vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_SYSENTER_ESP, MSR_TYPE_RW);
>> + vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_SYSENTER_EIP, MSR_TYPE_RW);
>> + if (kvm_cstate_in_guest(vmx->vcpu.kvm)) {
>> + vmx_disable_intercept_for_msr(msr_bitmap, MSR_CORE_C1_RES, MSR_TYPE_R);
>> + vmx_disable_intercept_for_msr(msr_bitmap, MSR_CORE_C3_RESIDENCY, MSR_TYPE_R);
>> + vmx_disable_intercept_for_msr(msr_bitmap, MSR_CORE_C6_RESIDENCY, MSR_TYPE_R);
>> + vmx_disable_intercept_for_msr(msr_bitmap, MSR_CORE_C7_RESIDENCY, MSR_TYPE_R);
>> + }
>> +
>> vmcs_write64(MSR_BITMAP, __pa(vmx->vmcs01.msr_bitmap));
>> + }
>> + vmx->msr_bitmap_mode = 0;
>
> Zeroing msr_bitmap_mode can be skipped as well.
>
>> vmcs_write64(VMCS_LINK_POINTER, -1ull); /* 22.3.1.5 */
>>
>> @@ -6074,7 +6091,8 @@ void vmx_set_virtual_apic_mode(struct kvm_vcpu *vcpu)
>> }
>> secondary_exec_controls_set(vmx, sec_exec_control);
>>
>> - vmx_update_msr_bitmap(vcpu);
>> + if (cpu_has_vmx_msr_bitmap())
>> + vmx_update_msr_bitmap(vcpu);
>> }
>>
>> static void vmx_set_apic_access_page_addr(struct kvm_vcpu *vcpu, hpa_t hpa)
>> @@ -6688,7 +6706,6 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
>> {
>> int err;
>> struct vcpu_vmx *vmx;
>> - unsigned long *msr_bitmap;
>> int i, cpu;
>>
>> BUILD_BUG_ON_MSG(offsetof(struct vcpu_vmx, vcpu) != 0,
>> @@ -6745,22 +6762,6 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
>> if (err < 0)
>> goto free_msrs;
>>
>> - msr_bitmap = vmx->vmcs01.msr_bitmap;
>> - vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_TSC, MSR_TYPE_R);
>> - vmx_disable_intercept_for_msr(msr_bitmap, MSR_FS_BASE, MSR_TYPE_RW);
>> - vmx_disable_intercept_for_msr(msr_bitmap, MSR_GS_BASE, MSR_TYPE_RW);
>> - vmx_disable_intercept_for_msr(msr_bitmap, MSR_KERNEL_GS_BASE, MSR_TYPE_RW);
>> - vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_SYSENTER_CS, MSR_TYPE_RW);
>> - vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_SYSENTER_ESP, MSR_TYPE_RW);
>> - vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_SYSENTER_EIP, MSR_TYPE_RW);
>> - if (kvm_cstate_in_guest(kvm)) {
>> - vmx_disable_intercept_for_msr(msr_bitmap, MSR_CORE_C1_RES, MSR_TYPE_R);
>> - vmx_disable_intercept_for_msr(msr_bitmap, MSR_CORE_C3_RESIDENCY, MSR_TYPE_R);
>> - vmx_disable_intercept_for_msr(msr_bitmap, MSR_CORE_C6_RESIDENCY, MSR_TYPE_R);
>> - vmx_disable_intercept_for_msr(msr_bitmap, MSR_CORE_C7_RESIDENCY, MSR_TYPE_R);
>> - }
>> - vmx->msr_bitmap_mode = 0;
>
> Keep this code here to be consistent with the previous change that moved
> the guest_msrs intialization *out* of the VMCS specific function. Both
> are collateral pages that are not directly part of the VMCS.
>
> I'd be tempted to use a goto to skip the code, the line length is bad
> enough as it is, e.g.:
>
> if (!cpu_has_vmx_msr_bitmap())
> goto skip_msr_bitmap;
>
> vmx->msr_bitmap_mode = 0;
> skip_msr_bitmap:
>
>> -
>> vmx->loaded_vmcs = &vmx->vmcs01;
>> cpu = get_cpu();
>> vmx_vcpu_load(&vmx->vcpu, cpu);
>> --
>> 2.19.1
>>
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