Re: [PATCH v6 28/64] KVM: arm64: nv: Emulate EL12 register accesses from the virtual EL2

Alexandru Elisei
2022-02-08T15:36:14Z

Hi Marc,

On Fri, Jan 28, 2022 at 12:18:36PM +0000, Marc Zyngier wrote:
> From: Jintack Lim <jintack.lim@linaro.org>
>
> With HCR_EL2.NV bit set, accesses to EL12 registers in the virtual EL2
> trap to EL2. Handle those traps just like we do for EL1 registers.
>
> One exception is CNTKCTL_EL12. We don't trap on CNTKCTL_EL1 for non-VHE
> virtual EL2 because we don't have to. However, accessing CNTKCTL_EL12
> will trap since it's one of the EL12 registers controlled by HCR_EL2.NV
> bit. Therefore, add a handler for it and don't treat it as a
> non-trap-registers when preparing a shadow context.
>
> These registers, being only a view on their EL1 counterpart, are
> permanently hidden from userspace.
>
> Signed-off-by: Jintack Lim <jintack.lim@linaro.org>
> [maz: EL12_REG(), register visibility]
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
> arch/arm64/kvm/sys_regs.c | 37 +++++++++++++++++++++++++++++++++++++
> 1 file changed, 37 insertions(+)
>
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 0c9bbe5eee5e..697bf0bca550 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -1634,6 +1634,26 @@ static unsigned int el2_visibility(const struct kvm_vcpu *vcpu,
> .val = v, \
> }
>
> +/*
> + * EL{0,1}2 registers are the EL2 view on an EL0 or EL1 register when
> + * HCR_EL2.E2H==1, and only in the sysreg table for convenience of
> + * handling traps. Given that, they are always hidden from userspace.
> + */
> +static unsigned int elx2_visibility(const struct kvm_vcpu *vcpu,
> + const struct sys_reg_desc *rd)
> +{
> + return REG_HIDDEN_USER;
> +}
> +
> +#define EL12_REG(name, acc, rst, v) { \
> + SYS_DESC(SYS_##name##_EL12), \
> + .access = acc, \
> + .reset = rst, \
> + .reg = name##_EL1, \
> + .val = v, \
> + .visibility = elx2_visibility, \
> +}
> +
> /* sys_reg_desc initialiser for known cpufeature ID registers */
> #define ID_SANITISED(name) { \
> SYS_DESC(SYS_##name), \
> @@ -2194,6 +2214,23 @@ static const struct sys_reg_desc sys_reg_descs[] = {
> EL2_REG(CNTVOFF_EL2, access_rw, reset_val, 0),
> EL2_REG(CNTHCTL_EL2, access_rw, reset_val, 0),
>
> + EL12_REG(SCTLR, access_vm_reg, reset_val, 0x00C50078),
> + EL12_REG(CPACR, access_rw, reset_val, 0),
> + EL12_REG(TTBR0, access_vm_reg, reset_unknown, 0),
> + EL12_REG(TTBR1, access_vm_reg, reset_unknown, 0),
> + EL12_REG(TCR, access_vm_reg, reset_val, 0),
> + { SYS_DESC(SYS_SPSR_EL12), access_spsr},
> + { SYS_DESC(SYS_ELR_EL12), access_elr},
> + EL12_REG(AFSR0, access_vm_reg, reset_unknown, 0),
> + EL12_REG(AFSR1, access_vm_reg, reset_unknown, 0),
> + EL12_REG(ESR, access_vm_reg, reset_unknown, 0),
> + EL12_REG(FAR, access_vm_reg, reset_unknown, 0),
> + EL12_REG(MAIR, access_vm_reg, reset_unknown, 0),
> + EL12_REG(AMAIR, access_vm_reg, reset_amair_el1, 0),
> + EL12_REG(VBAR, access_rw, reset_val, 0),
> + EL12_REG(CONTEXTIDR, access_vm_reg, reset_val, 0),
> + EL12_REG(CNTKCTL, access_rw, reset_val, 0),

Compared against Table D5-48 from ARM DDI 0487G.a (page D5-2768), everything
looks correct to me:

Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>

Thanks,
Alex

> +
> EL2_REG(SP_EL2, NULL, reset_unknown, 0),
> };
>
> --
> 2.30.2
>