linux-kernel - Re: [PATCH v2 07/32] KVM: x86: Use non-atomic bit ops to manipulate "shadow" MSR intercepts

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Message-ID: <ace63fad-647d-48ff-88bd-9029f9fe0adb@linux.intel.com>
Date: Wed, 11 Jun 2025 14:38:58 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
 linux-kernel@...r.kernel.org, Chao Gao <chao.gao@...el.com>,
 Borislav Petkov <bp@...en8.de>, Xin Li <xin@...or.com>,
 Dapeng Mi <dapeng1.mi@...ux.intel.com>,
 Francesco Lavra <francescolavra.fl@...il.com>,
 Manali Shukla <Manali.Shukla@....com>
Subject: Re: [PATCH v2 07/32] KVM: x86: Use non-atomic bit ops to manipulate
 "shadow" MSR intercepts



On 6/11/2025 6:57 AM, Sean Christopherson wrote:
> Manipulate the MSR bitmaps using non-atomic bit ops APIs (two underscores),
> as the bitmaps are per-vCPU and are only ever accessed while vcpu->mutex is
> held.
>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Binbin Wu <binbin.wu@...ux.intel.com>

> ---
>   arch/x86/kvm/svm/svm.c | 12 ++++++------
>   arch/x86/kvm/vmx/vmx.c |  8 ++++----
>   2 files changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 7e39b9df61f1..ec97ea1d7b38 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -789,14 +789,14 @@ static void set_shadow_msr_intercept(struct kvm_vcpu *vcpu, u32 msr, int read,
>   
>   	/* Set the shadow bitmaps to the desired intercept states */
>   	if (read)
> -		set_bit(slot, svm->shadow_msr_intercept.read);
> +		__set_bit(slot, svm->shadow_msr_intercept.read);
>   	else
> -		clear_bit(slot, svm->shadow_msr_intercept.read);
> +		__clear_bit(slot, svm->shadow_msr_intercept.read);
>   
>   	if (write)
> -		set_bit(slot, svm->shadow_msr_intercept.write);
> +		__set_bit(slot, svm->shadow_msr_intercept.write);
>   	else
> -		clear_bit(slot, svm->shadow_msr_intercept.write);
> +		__clear_bit(slot, svm->shadow_msr_intercept.write);
>   }
>   
>   static bool valid_msr_intercept(u32 index)
> @@ -862,8 +862,8 @@ static void set_msr_interception_bitmap(struct kvm_vcpu *vcpu, u32 *msrpm,
>   	bit_write = 2 * (msr & 0x0f) + 1;
>   	tmp       = msrpm[offset];
>   
> -	read  ? clear_bit(bit_read,  &tmp) : set_bit(bit_read,  &tmp);
> -	write ? clear_bit(bit_write, &tmp) : set_bit(bit_write, &tmp);
> +	read  ? __clear_bit(bit_read,  &tmp) : __set_bit(bit_read,  &tmp);
> +	write ? __clear_bit(bit_write, &tmp) : __set_bit(bit_write, &tmp);
>   
>   	msrpm[offset] = tmp;
>   
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 9ff00ae9f05a..8f7fe04a1998 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -4029,9 +4029,9 @@ void vmx_disable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type)
>   	idx = vmx_get_passthrough_msr_slot(msr);
>   	if (idx >= 0) {
>   		if (type & MSR_TYPE_R)
> -			clear_bit(idx, vmx->shadow_msr_intercept.read);
> +			__clear_bit(idx, vmx->shadow_msr_intercept.read);
>   		if (type & MSR_TYPE_W)
> -			clear_bit(idx, vmx->shadow_msr_intercept.write);
> +			__clear_bit(idx, vmx->shadow_msr_intercept.write);
>   	}
>   
>   	if ((type & MSR_TYPE_R) &&
> @@ -4071,9 +4071,9 @@ void vmx_enable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type)
>   	idx = vmx_get_passthrough_msr_slot(msr);
>   	if (idx >= 0) {
>   		if (type & MSR_TYPE_R)
> -			set_bit(idx, vmx->shadow_msr_intercept.read);
> +			__set_bit(idx, vmx->shadow_msr_intercept.read);
>   		if (type & MSR_TYPE_W)
> -			set_bit(idx, vmx->shadow_msr_intercept.write);
> +			__set_bit(idx, vmx->shadow_msr_intercept.write);
>   	}
>   
>   	if (type & MSR_TYPE_R)