RE: [PATCH v2] KVM: arm64: Make L1Ip feature in CTR_EL0 writable from userspace

[Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>]

Hi Oliver,

A gentle ping on this. I think it still applies cleanly on top of Joey's v6 of MPAM
Hide series.

Thanks,
Shameer

> -----Original Message-----
> From: linux-arm-kernel <linux-arm-kernel-bounces@lists.infradead.org> On
> Behalf Of Shameer Kolothum
> Sent: Tuesday, October 22, 2024 8:40 AM
> To: kvmarm@lists.linux.dev; maz@kernel.org; oliver.upton@linux.dev
> Cc: james.morse@arm.com; joey.gouly@arm.com;
> suzuki.poulose@arm.com; sebott@redhat.com; yuzenghui
> <yuzenghui@huawei.com>; Wangzhou (B) <wangzhou1@hisilicon.com>;
> linux-arm-kernel@lists.infradead.org; Linuxarm <linuxarm@huawei.com>
> Subject: [PATCH v2] KVM: arm64: Make L1Ip feature in CTR_EL0 writable
> from userspace
> 
> Only allow userspace to set VIPT(0b10) or PIPT(0b11) for L1Ip based on
> what hardware reports as both AIVIVT (0b01) and VPIPT (0b00) are
> documented as reserved.
> 
> Using a VIPT for Guest where hardware reports PIPT may lead to over
> invalidation, but is still correct. Hence, we can allow downgrading
> PIPT to VIPT, but not the other way around.
> 
> Reviewed-by: Sebastian Ott <sebott@redhat.com>
> Reviewed-by: Marc Zyngier <maz@kernel.org>
> Signed-off-by: Shameer Kolothum
> <shameerali.kolothum.thodi@huawei.com>
> ---
> v1:
> https://lore.kernel.org/kvmarm/20241017085925.40532-1-
> shameerali.kolothum.thodi@huawei.com/
> 
> Changes from v1:
>  -As per Marc's suggestion modified the way set_ctr_el0() restricted
>   the write which implied ordered values for the types. Instead
>   explicitly listed  all possible policy types.
>  -Added R-by tags(Thanks!).
> 
> Thanks,
> Shameer
> ---
>  arch/arm64/kvm/sys_regs.c | 38 ++++++++++++++++++++++++++++++++++---
> -
>  1 file changed, 34 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index d97ccf1c1558..0a0f336b0edd 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -1872,6 +1872,34 @@ static int set_id_aa64pfr1_el1(struct kvm_vcpu
> *vcpu,
>  	return set_id_reg(vcpu, rd, user_val);
>  }
> 
> +static int set_ctr_el0(struct kvm_vcpu *vcpu,
> +		       const struct sys_reg_desc *rd, u64 user_val)
> +{
> +	u8 user_L1Ip = SYS_FIELD_GET(CTR_EL0, L1Ip, user_val);
> +
> +	/*
> +	 * Both AIVIVT (0b01) and VPIPT (0b00) are documented as reserved.
> +	 * Hence only allow to set VIPT(0b10) or PIPT(0b11) for L1Ip based
> +	 * on what hardware reports.
> +	 *
> +	 * Using a VIPT software model on PIPT will lead to over
> invalidation,
> +	 * but still correct. Hence, we can allow downgrading PIPT to VIPT,
> +	 * but not the other way around. This is handled via
> arm64_ftr_safe_value()
> +	 * as CTR_EL0 ftr_bits has L1Ip field with type FTR_EXACT and safe
> value
> +	 * set as VIPT.
> +	 */
> +	switch (user_L1Ip) {
> +	case CTR_EL0_L1Ip_RESERVED_VPIPT:
> +	case CTR_EL0_L1Ip_RESERVED_AIVIVT:
> +		return -EINVAL;
> +	case CTR_EL0_L1Ip_VIPT:
> +	case CTR_EL0_L1Ip_PIPT:
> +		return set_id_reg(vcpu, rd, user_val);
> +	default:
> +		return -ENOENT;
> +	}
> +}
> +
>  /*
>   * cpufeature ID register user accessors
>   *
> @@ -2614,10 +2642,12 @@ static const struct sys_reg_desc sys_reg_descs[]
> = {
>  	{ SYS_DESC(SYS_CCSIDR2_EL1), undef_access },
>  	{ SYS_DESC(SYS_SMIDR_EL1), undef_access },
>  	{ SYS_DESC(SYS_CSSELR_EL1), access_csselr, reset_unknown,
> CSSELR_EL1 },
> -	ID_WRITABLE(CTR_EL0, CTR_EL0_DIC_MASK |
> -			     CTR_EL0_IDC_MASK |
> -			     CTR_EL0_DminLine_MASK |
> -			     CTR_EL0_IminLine_MASK),
> +	ID_FILTERED(CTR_EL0, ctr_el0,
> +		    CTR_EL0_DIC_MASK |
> +		    CTR_EL0_IDC_MASK |
> +		    CTR_EL0_DminLine_MASK |
> +		    CTR_EL0_L1Ip_MASK |
> +		    CTR_EL0_IminLine_MASK),
>  	{ SYS_DESC(SYS_SVCR), undef_access, reset_val, SVCR, 0, .visibility =
> sme_visibility  },
>  	{ SYS_DESC(SYS_FPMR), undef_access, reset_val, FPMR, 0, .visibility =
> fp8_visibility },
> 
> --
> 2.45.2
>