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

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On 06/21/2019 10:37 AM, Marc Zyngier wrote:
> From: Andre Przywara <andre.przywara@xxxxxxx>
> 
> 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@xxxxxxx>
> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
> ---
>  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__)

In this patch, find_el2_sysreg returns NULL for PURE_EL2 registers. So
for PURE_EL2, the access would go through the switch case. However this
branch suggest that for PURE_EL2 register we intend to do the read from
the memory backed version.

Which should it be?

> +				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);
> +	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;

As in the read case, this is never reached and we'll go through the
switch case.

Cheers,

-- 
Julien Thierry



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