linux-kernel - Re: [PATCH v17 1/7] arm/arm64: Probe for the presence of KVM hypervisor

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Date:   Fri, 5 Feb 2021 17:00:06 +0000
From:   Will Deacon <will@...nel.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Steven Price <steven.price@....com>, netdev@...r.kernel.org,
        yangbo.lu@....com, john.stultz@...aro.org, tglx@...utronix.de,
        pbonzini@...hat.com, seanjc@...gle.com, richardcochran@...il.com,
        Mark.Rutland@....com, suzuki.poulose@....com,
        Andre.Przywara@....com, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        kvm@...r.kernel.org, Steve.Capper@....com, justin.he@....com,
        jianyong.wu@....com, kernel-team@...roid.com
Subject: Re: [PATCH v17 1/7] arm/arm64: Probe for the presence of KVM
 hypervisor

On Fri, Feb 05, 2021 at 04:50:27PM +0000, Marc Zyngier wrote:
> On 2021-02-05 11:19, Will Deacon wrote:
> > On Fri, Feb 05, 2021 at 09:11:00AM +0000, Steven Price wrote:
> > > On 02/02/2021 14:11, Marc Zyngier wrote:
> > > > +	for (i = 0; i < 32; ++i) {
> > > > +		if (res.a0 & (i))
> > > > +			set_bit(i + (32 * 0), __kvm_arm_hyp_services);
> > > > +		if (res.a1 & (i))
> > > > +			set_bit(i + (32 * 1), __kvm_arm_hyp_services);
> > > > +		if (res.a2 & (i))
> > > > +			set_bit(i + (32 * 2), __kvm_arm_hyp_services);
> > > > +		if (res.a3 & (i))
> > > > +			set_bit(i + (32 * 3), __kvm_arm_hyp_services);
> > > 
> > > The bit shifts are missing, the tests should be of the form:
> > > 
> > > 	if (res.a0 & (1 << i))
> > > 
> > > Or indeed using a BIT() macro.
> > 
> > Maybe even test_bit()?
> 
> Actually, maybe not doing things a-bit-at-a-time is less error prone.
> See below what I intend to fold in.
> 
> Thanks,
> 
>         M.
> 
> diff --git a/drivers/firmware/smccc/kvm_guest.c
> b/drivers/firmware/smccc/kvm_guest.c
> index 00bf3c7969fc..08836f2f39ee 100644
> --- a/drivers/firmware/smccc/kvm_guest.c
> +++ b/drivers/firmware/smccc/kvm_guest.c
> @@ -2,8 +2,8 @@
> 
>  #define pr_fmt(fmt) "smccc: KVM: " fmt
> 
> -#include <linux/init.h>
>  #include <linux/arm-smccc.h>
> +#include <linux/bitmap.h>
>  #include <linux/kernel.h>
>  #include <linux/string.h>
> 
> @@ -13,8 +13,8 @@ static DECLARE_BITMAP(__kvm_arm_hyp_services,
> ARM_SMCCC_KVM_NUM_FUNCS) __ro_afte
> 
>  void __init kvm_init_hyp_services(void)
>  {
> -	int i;
>  	struct arm_smccc_res res;
> +	u32 val[4];
> 
>  	if (arm_smccc_1_1_get_conduit() != SMCCC_CONDUIT_HVC)
>  		return;
> @@ -28,16 +28,13 @@ void __init kvm_init_hyp_services(void)
> 
>  	memset(&res, 0, sizeof(res));
>  	arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_FEATURES_FUNC_ID, &res);
> -	for (i = 0; i < 32; ++i) {
> -		if (res.a0 & (i))
> -			set_bit(i + (32 * 0), __kvm_arm_hyp_services);
> -		if (res.a1 & (i))
> -			set_bit(i + (32 * 1), __kvm_arm_hyp_services);
> -		if (res.a2 & (i))
> -			set_bit(i + (32 * 2), __kvm_arm_hyp_services);
> -		if (res.a3 & (i))
> -			set_bit(i + (32 * 3), __kvm_arm_hyp_services);
> -	}
> +
> +	val[0] = lower_32_bits(res.a0);
> +	val[1] = lower_32_bits(res.a1);
> +	val[2] = lower_32_bits(res.a2);
> +	val[3] = lower_32_bits(res.a3);
> +
> +	bitmap_from_arr32(__kvm_arm_hyp_services, val, ARM_SMCCC_KVM_NUM_FUNCS);

Nice! That's loads better.

Will