linux-kernel - Re: [PATCH v1 1/4] KVM/vmx: re-write the msr auto switch feature

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Date:   Mon, 25 Sep 2017 13:54:37 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wei Wang <wei.w.wang@...el.com>,
        virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, mst@...hat.com, rkrcmar@...hat.com,
        ak@...ux.intel.com, mingo@...hat.com
Subject: Re: [PATCH v1 1/4] KVM/vmx: re-write the msr auto switch feature

On 25/09/2017 06:44, Wei Wang wrote:
>  
> +static void update_msr_autoload_count_max(void)
> +{
> +	u64 vmx_msr;
> +	int n;
> +
> +	/*
> +	 * According to the Intel SDM, if Bits 27:25 of MSR_IA32_VMX_MISC is
> +	 * n, then (n + 1) * 512 is the recommended max number of MSRs to be
> +	 * included in the VMExit and VMEntry MSR auto switch list.
> +	 */
> +	rdmsrl(MSR_IA32_VMX_MISC, vmx_msr);
> +	n = ((vmx_msr & 0xe000000) >> 25) + 1;
> +	msr_autoload_count_max = n * KVM_VMX_DEFAULT_MSR_AUTO_LOAD_COUNT;
> +}
> +


Any reasons to do this if it's unlikely that we'll ever update more than
512 MSRs?

Paolo