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    SubjectRe: [PATCH v6 4/6] arm64/kvm: add a userspace option to enable pointer authentication
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    Hi James,

    On 2/27/19 12:03 AM, James Morse wrote:
    > Hi Amit,
    >
    > On 19/02/2019 09:24, Amit Daniel Kachhap wrote:
    >> This feature will allow the KVM guest to allow the handling of
    >> pointer authentication instructions or to treat them as undefined
    >> if not set. It uses the existing vcpu API KVM_ARM_VCPU_INIT to
    >> supply this parameter instead of creating a new API.
    >>
    >> A new register is not created to pass this parameter via
    >> SET/GET_ONE_REG interface as just a flag (KVM_ARM_VCPU_PTRAUTH)
    >> supplied is enough to enable this feature.
    >
    > and an attempt to restore the id register with the other version would fail.
    >
    >
    >> diff --git a/Documentation/arm64/pointer-authentication.txt b/Documentation/arm64/pointer-authentication.txt
    >> index a25cd21..0529a7d 100644
    >> --- a/Documentation/arm64/pointer-authentication.txt
    >> +++ b/Documentation/arm64/pointer-authentication.txt
    >> @@ -82,7 +82,8 @@ pointers).
    >> Virtualization
    >> --------------
    >>
    >> -Pointer authentication is not currently supported in KVM guests. KVM
    >> -will mask the feature bits from ID_AA64ISAR1_EL1, and attempted use of
    >> -the feature will result in an UNDEFINED exception being injected into
    >> -the guest.
    >
    >> +Pointer authentication is enabled in KVM guest when virtual machine is
    >> +created by passing a flag (KVM_ARM_VCPU_PTRAUTH)
    >
    > (This is still mixing VM and VCPU)
    >
    >
    >> + requesting this feature to be enabled.
    >
    > .. on each vcpu?
    >
    >
    >> +Without this flag, pointer authentication is not enabled
    >> +in KVM guests and attempted use of the feature will result in an UNDEFINED
    >> +exception being injected into the guest.
    >
    > 'guests' here suggests its a VM property. If you set it on some VCPU but not others KVM
    > will generate undefs instead of enabling the feature. (which is the right thing to do)
    >
    > I think it needs to be clear this is a per-vcpu property.
    ok.
    >
    >
    >> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
    >> index 97c3478..5f82ca1 100644
    >> --- a/arch/arm64/include/uapi/asm/kvm.h
    >> +++ b/arch/arm64/include/uapi/asm/kvm.h
    >> @@ -102,6 +102,7 @@ struct kvm_regs {
    >> #define KVM_ARM_VCPU_EL1_32BIT 1 /* CPU running a 32bit VM */
    >> #define KVM_ARM_VCPU_PSCI_0_2 2 /* CPU uses PSCI v0.2 */
    >> #define KVM_ARM_VCPU_PMU_V3 3 /* Support guest PMUv3 */
    >
    >> +#define KVM_ARM_VCPU_PTRAUTH 4 /* VCPU uses address authentication */
    >
    > Just address authentication? I agree with Mark we should have two bits to match what gets
    > exposed to EL0. One would then be address, the other generic.
    ok.
    >
    >
    >> diff --git a/arch/arm64/kvm/hyp/ptrauth-sr.c b/arch/arm64/kvm/hyp/ptrauth-sr.c
    >> index 528ee6e..6846a23 100644
    >> --- a/arch/arm64/kvm/hyp/ptrauth-sr.c
    >> +++ b/arch/arm64/kvm/hyp/ptrauth-sr.c
    >> @@ -93,9 +93,23 @@ void kvm_arm_vcpu_ptrauth_reset(struct kvm_vcpu *vcpu)
    >
    >> +/**
    >> + * kvm_arm_vcpu_ptrauth_allowed - checks if ptrauth feature is allowed by user
    >> + *
    >> + * @vcpu: The VCPU pointer
    >> + *
    >> + * This function will be used to check userspace option to have ptrauth or not
    >> + * in the guest kernel.
    >> + */
    >> +bool kvm_arm_vcpu_ptrauth_allowed(const struct kvm_vcpu *vcpu)
    >> +{
    >> + return kvm_supports_ptrauth() &&
    >> + test_bit(KVM_ARM_VCPU_PTRAUTH, vcpu->arch.features);
    >> +}
    >
    > This isn't used from world-switch, could it be moved to guest.c?
    yes sure.
    >
    >
    >> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
    >> index 12529df..f7bcc60 100644
    >> --- a/arch/arm64/kvm/sys_regs.c
    >> +++ b/arch/arm64/kvm/sys_regs.c
    >> @@ -1055,7 +1055,7 @@ static bool access_cntp_cval(struct kvm_vcpu *vcpu,
    >> }
    >>
    >> /* Read a sanitised cpufeature ID register by sys_reg_desc */
    >> -static u64 read_id_reg(struct sys_reg_desc const *r, bool raz)
    >> +static u64 read_id_reg(struct kvm_vcpu *vcpu, struct sys_reg_desc const *r, bool raz)
    >
    > (It might be easier on the reviewer to move these mechanical changes to an earlier patch)
    Yes with including some of Dave SVE patches this wont be required.

    Thanks,
    Amit D
    >
    >
    > Looks good,
    >
    > Thanks,
    >
    > James
    >

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