Re: [PATCH 13/59] KVM: arm64: nv: Handle virtual EL2 registers in vcpu_read/write_sys_reg()

Alexandru Elisei
2019-06-26T15:04:19Z

On 6/21/19 10:37 AM, Marc Zyngier wrote:
> From: Andre Przywara <andre.przywara@arm.com>
>
> KVM internally uses accessor functions when reading or writing the
> guest's system registers. This takes care of accessing either the stored
> copy or using the "live" EL1 system registers when the host uses VHE.
>
> With the introduction of virtual EL2 we add a bunch of EL2 system
> registers, which now must also be taken care of:
> - If the guest is running in vEL2, and we access an EL1 sysreg, we must
> revert to the stored version of that, and not use the CPU's copy.
> - If the guest is running in vEL1, and we access an EL2 sysreg, we must
> also use the stored version, since the CPU carries the EL1 copy.
> - Some EL2 system registers are supposed to affect the current execution
> of the system, so we need to put them into their respective EL1
> counterparts. For this we need to define a mapping between the two.
> This is done using the newly introduced struct el2_sysreg_map.
> - Some EL2 system registers have a different format than their EL1
> counterpart, so we need to translate them before writing them to the
> CPU. This is done using an (optional) translate function in the map.
> - There are the three special registers SP_EL2, SPSR_EL2 and ELR_EL2,
> which need some separate handling.
>
> All of these cases are now wrapped into the existing accessor functions,
> so KVM users wouldn't need to care whether they access EL2 or EL1
> registers and also which state the guest is in.
>
> This handles what was formerly known as the "shadow state" dynamically,
> without requiring a separate copy for each vCPU EL.
>
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
> arch/arm64/include/asm/kvm_emulate.h | 6 +
> arch/arm64/include/asm/kvm_host.h | 5 +
> arch/arm64/kvm/sys_regs.c | 163 +++++++++++++++++++++++++++
> 3 files changed, 174 insertions(+)
>
> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> index c43aac5fed69..f37006b6eec4 100644
> --- a/arch/arm64/include/asm/kvm_emulate.h
> +++ b/arch/arm64/include/asm/kvm_emulate.h
> @@ -70,6 +70,12 @@ void kvm_emulate_nested_eret(struct kvm_vcpu *vcpu);
> int kvm_inject_nested_sync(struct kvm_vcpu *vcpu, u64 esr_el2);
> int kvm_inject_nested_irq(struct kvm_vcpu *vcpu);
>
> +u64 translate_tcr(u64 tcr);
> +u64 translate_cptr(u64 tcr);
> +u64 translate_sctlr(u64 tcr);
> +u64 translate_ttbr0(u64 tcr);
> +u64 translate_cnthctl(u64 tcr);
> +
> static inline bool vcpu_el1_is_32bit(struct kvm_vcpu *vcpu)
> {
> return !(vcpu->arch.hcr_el2 & HCR_RW);
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 2d4290d2513a..dae9c42a7219 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -217,6 +217,11 @@ enum vcpu_sysreg {
> NR_SYS_REGS /* Nothing after this line! */
> };
>
> +static inline bool sysreg_is_el2(int reg)
> +{
> + return reg >= FIRST_EL2_SYSREG && reg < NR_SYS_REGS;
> +}
> +
> /* 32bit mapping */
> #define c0_MPIDR (MPIDR_EL1 * 2) /* MultiProcessor ID Register */
> #define c0_CSSELR (CSSELR_EL1 * 2)/* Cache Size Selection Register */
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 693dd063c9c2..d024114da162 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -76,11 +76,142 @@ static bool write_to_read_only(struct kvm_vcpu *vcpu,
> return false;
> }
>
> +static u64 tcr_el2_ips_to_tcr_el1_ps(u64 tcr_el2)
> +{
> + return ((tcr_el2 & TCR_EL2_PS_MASK) >> TCR_EL2_PS_SHIFT)
> + << TCR_IPS_SHIFT;
> +}
> +
> +u64 translate_tcr(u64 tcr)
> +{
> + return TCR_EPD1_MASK | /* disable TTBR1_EL1 */
> + ((tcr & TCR_EL2_TBI) ? TCR_TBI0 : 0) |
> + tcr_el2_ips_to_tcr_el1_ps(tcr) |
> + (tcr & TCR_EL2_TG0_MASK) |
> + (tcr & TCR_EL2_ORGN0_MASK) |
> + (tcr & TCR_EL2_IRGN0_MASK) |
> + (tcr & TCR_EL2_T0SZ_MASK);
> +}
> +
> +u64 translate_cptr(u64 cptr_el2)
> +{
> + u64 cpacr_el1 = 0;
> +
> + if (!(cptr_el2 & CPTR_EL2_TFP))
> + cpacr_el1 |= CPACR_EL1_FPEN;
> + if (cptr_el2 & CPTR_EL2_TTA)
> + cpacr_el1 |= CPACR_EL1_TTA;
> + if (!(cptr_el2 & CPTR_EL2_TZ))
> + cpacr_el1 |= CPACR_EL1_ZEN;
> +
> + return cpacr_el1;
> +}
> +
> +u64 translate_sctlr(u64 sctlr)
> +{
> + /* Bit 20 is RES1 in SCTLR_EL1, but RES0 in SCTLR_EL2 */
> + return sctlr | BIT(20);
> +}
> +
> +u64 translate_ttbr0(u64 ttbr0)
> +{
> + /* Force ASID to 0 (ASID 0 or RES0) */
> + return ttbr0 & ~GENMASK_ULL(63, 48);
> +}
> +
> +u64 translate_cnthctl(u64 cnthctl)
> +{
> + return ((cnthctl & 0x3) << 10) | (cnthctl & 0xfc);
> +}
> +
> +#define EL2_SYSREG(el2, el1, translate) \
> + [el2 - FIRST_EL2_SYSREG] = { el2, el1, translate }
> +#define PURE_EL2_SYSREG(el2) \
> + [el2 - FIRST_EL2_SYSREG] = { el2,__INVALID_SYSREG__, NULL }
> +/*
> + * Associate vEL2 registers to their EL1 counterparts on the CPU.
> + * The translate function can be NULL, when the register layout is identical.
> + */
> +struct el2_sysreg_map {
> + int sysreg; /* EL2 register index into the array above */
> + int mapping; /* associated EL1 register */
> + u64 (*translate)(u64 value);
> +} nested_sysreg_map[NR_SYS_REGS - FIRST_EL2_SYSREG] = {
> + PURE_EL2_SYSREG( VPIDR_EL2 ),
> + PURE_EL2_SYSREG( VMPIDR_EL2 ),
> + PURE_EL2_SYSREG( ACTLR_EL2 ),
> + PURE_EL2_SYSREG( HCR_EL2 ),
> + PURE_EL2_SYSREG( MDCR_EL2 ),
> + PURE_EL2_SYSREG( HSTR_EL2 ),
> + PURE_EL2_SYSREG( HACR_EL2 ),
> + PURE_EL2_SYSREG( VTTBR_EL2 ),
> + PURE_EL2_SYSREG( VTCR_EL2 ),
> + PURE_EL2_SYSREG( RVBAR_EL2 ),
> + PURE_EL2_SYSREG( RMR_EL2 ),
> + PURE_EL2_SYSREG( TPIDR_EL2 ),
> + PURE_EL2_SYSREG( CNTVOFF_EL2 ),
> + PURE_EL2_SYSREG( CNTHCTL_EL2 ),
> + PURE_EL2_SYSREG( HPFAR_EL2 ),
> + EL2_SYSREG( SCTLR_EL2, SCTLR_EL1, translate_sctlr ),
> + EL2_SYSREG( CPTR_EL2, CPACR_EL1, translate_cptr ),
> + EL2_SYSREG( TTBR0_EL2, TTBR0_EL1, translate_ttbr0 ),
> + EL2_SYSREG( TTBR1_EL2, TTBR1_EL1, NULL ),
> + EL2_SYSREG( TCR_EL2, TCR_EL1, translate_tcr ),
> + EL2_SYSREG( VBAR_EL2, VBAR_EL1, NULL ),
> + EL2_SYSREG( AFSR0_EL2, AFSR0_EL1, NULL ),
> + EL2_SYSREG( AFSR1_EL2, AFSR1_EL1, NULL ),
> + EL2_SYSREG( ESR_EL2, ESR_EL1, NULL ),
> + EL2_SYSREG( FAR_EL2, FAR_EL1, NULL ),
> + EL2_SYSREG( MAIR_EL2, MAIR_EL1, NULL ),
> + EL2_SYSREG( AMAIR_EL2, AMAIR_EL1, NULL ),
> +};
> +
> +static
> +const struct el2_sysreg_map *find_el2_sysreg(const struct el2_sysreg_map *map,
> + int reg)
> +{
> + const struct el2_sysreg_map *entry;
> +
> + if (!sysreg_is_el2(reg))
> + return NULL;
> +
> + entry = &nested_sysreg_map[reg - FIRST_EL2_SYSREG];
> + if (entry->sysreg == __INVALID_SYSREG__)
> + return NULL;
> +
> + return entry;
> +}
> +
> u64 vcpu_read_sys_reg(const struct kvm_vcpu *vcpu, int reg)
> {
> +
> if (!vcpu->arch.sysregs_loaded_on_cpu)
> goto immediate_read;
>
> + if (unlikely(sysreg_is_el2(reg))) {
> + const struct el2_sysreg_map *el2_reg;
> +
> + if (!is_hyp_ctxt(vcpu))
> + goto immediate_read;
> +
> + el2_reg = find_el2_sysreg(nested_sysreg_map, reg);
> + if (el2_reg) {
> + /*
> + * If this register does not have an EL1 counterpart,
> + * then read the stored EL2 version.
> + */
> + if (el2_reg->mapping == __INVALID_SYSREG__)
> + goto immediate_read;
> +
> + /* Get the current version of the EL1 counterpart. */
> + reg = el2_reg->mapping;
> + }
> + } else {
> + /* EL1 register can't be on the CPU if the guest is in vEL2. */
> + if (unlikely(is_hyp_ctxt(vcpu)))
> + goto immediate_read;
> + }
> +
> /*
> * System registers listed in the switch are not saved on every
> * exit from the guest but are only saved on vcpu_put.
> @@ -114,6 +245,8 @@ u64 vcpu_read_sys_reg(const struct kvm_vcpu *vcpu, int reg)
> case DACR32_EL2: return read_sysreg_s(SYS_DACR32_EL2);
> case IFSR32_EL2: return read_sysreg_s(SYS_IFSR32_EL2);
> case DBGVCR32_EL2: return read_sysreg_s(SYS_DBGVCR32_EL2);
> + case SP_EL2: return read_sysreg(sp_el1);
From ARM DDI 0487D.b, section Behavior when HCR_EL2.NV == 1: "Reads or writes to
any allocated and implemented System register or Special-purpose register named
*_EL2, *_EL02, or *_EL12 in the MRS or MSR instruction, other than SP_EL2, are
trapped to EL2 rather than being UNDEFINED" (page D5-2480). My interpretation of
the text is that attempted reads of SP_EL2 from virtual EL2 cause an undefined
instruction exception.
> + case ELR_EL2: return read_sysreg_el1(SYS_ELR);
> }
>
> immediate_read:
> @@ -125,6 +258,34 @@ void vcpu_write_sys_reg(struct kvm_vcpu *vcpu, u64 val, int reg)
> if (!vcpu->arch.sysregs_loaded_on_cpu)
> goto immediate_write;
>
> + if (unlikely(sysreg_is_el2(reg))) {
> + const struct el2_sysreg_map *el2_reg;
> +
> + if (!is_hyp_ctxt(vcpu))
> + goto immediate_write;
> +
> + /* Store the EL2 version in the sysregs array. */
> + __vcpu_sys_reg(vcpu, reg) = val;
> +
> + el2_reg = find_el2_sysreg(nested_sysreg_map, reg);
> + if (el2_reg) {
> + /* Does this register have an EL1 counterpart? */
> + if (el2_reg->mapping == __INVALID_SYSREG__)
> + return;
> +
> + if (!vcpu_el2_e2h_is_set(vcpu) &&
> + el2_reg->translate)
> + val = el2_reg->translate(val);
> +
> + /* Redirect this to the EL1 version of the register. */
> + reg = el2_reg->mapping;
> + }
> + } else {
> + /* EL1 register can't be on the CPU if the guest is in vEL2. */
> + if (unlikely(is_hyp_ctxt(vcpu)))
> + goto immediate_write;
> + }
> +
> /*
> * System registers listed in the switch are not restored on every
> * entry to the guest but are only restored on vcpu_load.
> @@ -157,6 +318,8 @@ void vcpu_write_sys_reg(struct kvm_vcpu *vcpu, u64 val, int reg)
> case DACR32_EL2: write_sysreg_s(val, SYS_DACR32_EL2); return;
> case IFSR32_EL2: write_sysreg_s(val, SYS_IFSR32_EL2); return;
> case DBGVCR32_EL2: write_sysreg_s(val, SYS_DBGVCR32_EL2); return;
> + case SP_EL2: write_sysreg(val, sp_el1); return;
> + case ELR_EL2: write_sysreg_el1(val, SYS_ELR); return;
> }
>