Re: [PATCH -v5.1] x86/kvm: Implement HWCR support

[Sean Christopherson <sean.j.christopherson@intel.com>]

On Thu, Apr 18, 2019 at 04:19:49PM +0200, Borislav Petkov wrote:
> On Thu, Apr 18, 2019 at 06:56:06AM -0700, Sean Christopherson wrote:
> > This doesn't allow writing '0' regardless of msr_hwcr.BIT(18), which was
> > previously supported.
> 
> Restored the old conditional:
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 10f6acc6494c..f74f1280745b 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2318,7 +2318,8 @@ static int set_msr_mce(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  				return -1;
>  
>  			/* MCi_STATUS */
> -			if ((offset & 0x3) == 1 && !msr_info->host_initiated) {
> +			if (!msr_info->host_initiated &&
> +			    (offset & 0x3) == 1 && data != 0) {
>  				if (!can_set_mci_status(vcpu))
>  					return -1;
>  			}
> 
> > And there's no need for multiple if statements.
> 
> It is a bit more readable this way.
> 
> Actually, I'd break that if above into smaller if-statements with
> flipped logic to make it even more readable:
> 
> 	if (msr_info->host_initiated)
> 		goto set_msr;
> 
> 	if (!(offset & 0x3))
> 		goto set_msr;
> 
> 	if (!data)
> 		goto set_msr;
> 
> 	if (!can_set_mci_status(vcpu))
> 		return -1;

At that point it probably makes sense to rework the whole block as there
are existing issues in both the CTL and STATUS flows:

  - Fault cases should return '1', not '-1'.

  - host_initiated should be checked for the CTL case


My personal preference would be to combine the host_initiated and !data
checks for brevity, so something like:

	if (msr_info->host_initiated || !data)
		goto set_msr;

	offset = msr - MSR_IA32_MC0_CTL;
	if ((offset & 0x3) == 0 && (data | (1 << 10)) != ~(u64)0)
		return 1;
	if ((offset & 0x3) == 1 && !can_set_mci_status(vcpu))
		return 1;

set_msr:

> 
> set_msr:
> 	...
> 
> 
> Anything else? Can I send v5.2 now?
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> Good mailing practices for 400: avoid top-posting and trim the reply.