Re: [PATCH v6 39/64] KVM: arm64: nv: Set a handler for the system instruction traps

Alexandru Elisei
2022-02-24T11:59:04Z

Hi,

On Fri, Jan 28, 2022 at 12:18:47PM +0000, Marc Zyngier wrote:
> From: Jintack Lim <jintack.lim@linaro.org>
>
> When HCR.NV bit is set, execution of the EL2 translation regime address
> aranslation instructions and TLB maintenance instructions are trapped to
> EL2. In addition, execution of the EL1 translation regime address
> aranslation instructions and TLB maintenance instructions that are only
> accessible from EL2 and above are trapped to EL2. In these cases,
> ESR_EL2.EC will be set to 0x18.
>
> Rework the system instruction emulation framework to handle potentially
> all system instruction traps other than MSR/MRS instructions. Those
> system instructions would be AT and TLBI instructions controlled by
> HCR_EL2.NV, AT, and TTLB bits.
>
> Signed-off-by: Jintack Lim <jintack.lim@linaro.org>
> [maz: squashed two patches together, redispatched various bits around]
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
> arch/arm64/include/asm/kvm_host.h | 4 +--
> arch/arm64/kvm/handle_exit.c | 2 +-
> arch/arm64/kvm/sys_regs.c | 48 +++++++++++++++++++++++++------
> 3 files changed, 42 insertions(+), 12 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index a15183d0e1bf..0b887364f994 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -407,7 +407,7 @@ struct kvm_vcpu_arch {
> /*
> * Guest registers we preserve during guest debugging.
> *
> - * These shadow registers are updated by the kvm_handle_sys_reg
> + * These shadow registers are updated by the kvm_handle_sys
> * trap handler if the guest accesses or updates them while we
> * are using guest debug.
> */
> @@ -724,7 +724,7 @@ int kvm_handle_cp14_32(struct kvm_vcpu *vcpu);
> int kvm_handle_cp14_64(struct kvm_vcpu *vcpu);
> int kvm_handle_cp15_32(struct kvm_vcpu *vcpu);
> int kvm_handle_cp15_64(struct kvm_vcpu *vcpu);
> -int kvm_handle_sys_reg(struct kvm_vcpu *vcpu);
> +int kvm_handle_sys(struct kvm_vcpu *vcpu);
>
> void kvm_reset_sys_regs(struct kvm_vcpu *vcpu);
>
> diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> index 867de65eb766..d135fc7e6883 100644
> --- a/arch/arm64/kvm/handle_exit.c
> +++ b/arch/arm64/kvm/handle_exit.c
> @@ -236,7 +236,7 @@ static exit_handle_fn arm_exit_handlers[] = {
> [ESR_ELx_EC_SMC32] = handle_smc,
> [ESR_ELx_EC_HVC64] = handle_hvc,
> [ESR_ELx_EC_SMC64] = handle_smc,
> - [ESR_ELx_EC_SYS64] = kvm_handle_sys_reg,
> + [ESR_ELx_EC_SYS64] = kvm_handle_sys,
> [ESR_ELx_EC_SVE] = handle_sve,
> [ESR_ELx_EC_ERET] = kvm_handle_eret,
> [ESR_ELx_EC_IABT_LOW] = kvm_handle_guest_abort,
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 5e8876177ce6..f669618f966b 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -1771,10 +1771,6 @@ static bool access_spsr_el2(struct kvm_vcpu *vcpu,
> * more demanding guest...
> */
> static const struct sys_reg_desc sys_reg_descs[] = {
> - { SYS_DESC(SYS_DC_ISW), access_dcsw },
> - { SYS_DESC(SYS_DC_CSW), access_dcsw },
> - { SYS_DESC(SYS_DC_CISW), access_dcsw },
> -
> DBG_BCR_BVR_WCR_WVR_EL1(0),
> DBG_BCR_BVR_WCR_WVR_EL1(1),
> { SYS_DESC(SYS_MDCCINT_EL1), trap_debug_regs, reset_val, MDCCINT_EL1, 0 },
> @@ -2240,6 +2236,14 @@ static const struct sys_reg_desc sys_reg_descs[] = {
> EL2_REG(SP_EL2, NULL, reset_unknown, 0),
> };
>
> +#define SYS_INSN_TO_DESC(insn, access_fn, forward_fn) \
> + { SYS_DESC((insn)), (access_fn), NULL, 0, 0, NULL, NULL, (forward_fn) }

This macro looks out of place: it's not used anywhere in this patch, and the
next patch deletes it.

> +static struct sys_reg_desc sys_insn_descs[] = {
> + { SYS_DESC(SYS_DC_ISW), access_dcsw },
> + { SYS_DESC(SYS_DC_CSW), access_dcsw },
> + { SYS_DESC(SYS_DC_CISW), access_dcsw },
> +};
> +
> static bool trap_dbgdidr(struct kvm_vcpu *vcpu,
> struct sys_reg_params *p,
> const struct sys_reg_desc *r)
> @@ -2786,6 +2790,24 @@ static int emulate_sys_reg(struct kvm_vcpu *vcpu,
> return 1;
> }
>
> +static int emulate_sys_instr(struct kvm_vcpu *vcpu, struct sys_reg_params *p)
> +{
> + const struct sys_reg_desc *r;
> +
> + /* Search from the system instruction table. */
> + r = find_reg(p, sys_insn_descs, ARRAY_SIZE(sys_insn_descs));
> +
> + if (likely(r)) {
> + perform_access(vcpu, p, r);
> + } else {
> + kvm_err("Unsupported guest sys instruction at: %lx\n",
> + *vcpu_pc(vcpu));
> + print_sys_reg_instr(p);
> + kvm_inject_undefined(vcpu);
> + }
> + return 1;
> +}
> +
> /**
> * kvm_reset_sys_regs - sets system registers to reset value
> * @vcpu: The VCPU pointer
> @@ -2803,10 +2825,11 @@ void kvm_reset_sys_regs(struct kvm_vcpu *vcpu)
> }
>
> /**
> - * kvm_handle_sys_reg -- handles a mrs/msr trap on a guest sys_reg access
> + * kvm_handle_sys-- handles a system instruction or mrs/msr instruction trap
> + on a guest execution
> * @vcpu: The VCPU pointer
> */
> -int kvm_handle_sys_reg(struct kvm_vcpu *vcpu)
> +int kvm_handle_sys(struct kvm_vcpu *vcpu)
> {
> struct sys_reg_params params;
> unsigned long esr = kvm_vcpu_get_esr(vcpu);
> @@ -2818,10 +2841,16 @@ int kvm_handle_sys_reg(struct kvm_vcpu *vcpu)
> params = esr_sys64_to_params(esr);
> params.regval = vcpu_get_reg(vcpu, Rt);
>
> - ret = emulate_sys_reg(vcpu, &params);
> + if (params.Op0 == 1) {
> + /* System instructions */
> + ret = emulate_sys_instr(vcpu, &params);
> + } else {

This doesn't look right: according to ARM DDI 0487G.a, page C5-393, Op0 =
{0,2} represents instruction classes different from system register
accesses, yet KVM puts them in the same bucket as system register traps.

May I suggest this change:

if (params.Op0 == 3) {
/* do emulate_sys_reg() */
} else {
/* do emulate_sys_instr() */
}

Thanks,
Alex

> + /* MRS/MSR instructions */
> + ret = emulate_sys_reg(vcpu, &params);
> + if (!params.is_write)
> + vcpu_set_reg(vcpu, Rt, params.regval);
> + }
>
> - if (!params.is_write)
> - vcpu_set_reg(vcpu, Rt, params.regval);
> return ret;
> }
>
> @@ -3237,6 +3266,7 @@ void kvm_sys_reg_table_init(void)
> BUG_ON(check_sysreg_table(cp15_regs, ARRAY_SIZE(cp15_regs), true));
> BUG_ON(check_sysreg_table(cp15_64_regs, ARRAY_SIZE(cp15_64_regs), true));
> BUG_ON(check_sysreg_table(invariant_sys_regs, ARRAY_SIZE(invariant_sys_regs), false));
> + BUG_ON(check_sysreg_table(sys_insn_descs, ARRAY_SIZE(sys_insn_descs), false));
>
> /* We abuse the reset function to overwrite the table itself. */
> for (i = 0; i < ARRAY_SIZE(invariant_sys_regs); i++)
> --
> 2.30.2
>