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 11:19:22 +0000
From:   Will Deacon <will@...nel.org>
To:     Steven Price <steven.price@....com>
Cc:     Marc Zyngier <maz@...nel.org>, 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 09:11:00AM +0000, Steven Price wrote:
> On 02/02/2021 14:11, Marc Zyngier wrote:
> > diff --git a/drivers/firmware/smccc/kvm_guest.c b/drivers/firmware/smccc/kvm_guest.c
> > new file mode 100644
> > index 000000000000..23ce1ded88b4
> > --- /dev/null
> > +++ b/drivers/firmware/smccc/kvm_guest.c
> > @@ -0,0 +1,51 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +#define pr_fmt(fmt) "smccc: KVM: " fmt
> > +
> > +#include <linux/init.h>
> > +#include <linux/arm-smccc.h>
> > +#include <linux/kernel.h>
> > +#include <linux/string.h>
> > +
> > +static DECLARE_BITMAP(__kvm_arm_hyp_services, ARM_SMCCC_KVM_NUM_FUNCS) __ro_after_init = { };
> > +
> > +void __init kvm_init_hyp_services(void)
> > +{
> > +	int i;
> > +	struct arm_smccc_res res;
> > +
> > +	if (arm_smccc_1_1_get_conduit() != SMCCC_CONDUIT_HVC)
> > +		return;
> > +
> > +	arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID, &res);
> > +	if (res.a0 != ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_0 ||
> > +	    res.a1 != ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_1 ||
> > +	    res.a2 != ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_2 ||
> > +	    res.a3 != ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_3)
> > +		return;
> > +
> > +	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);
> 
> 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()?

Will