Re: [PATCH v2 7/9] arm64: KVM: add trap handlers for AArch32 debug registers

Marc Zyngier
2014-05-28T16:00:56Z

On 25/05/14 16:35, Christoffer Dall wrote:
> On Tue, May 20, 2014 at 05:55:43PM +0100, Marc Zyngier wrote:
>> Add handlers for all the AArch32 debug registers that are accessible
>> from EL0 or EL1. The code follow the same strategy as the AArch64
>> counterpart with regards to tracking the dirty state of the debug
>> registers.
>>
>> Reviewed-by: Anup Patel <anup.patel@linaro.org>
>> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
>> ---
>> arch/arm64/include/asm/kvm_asm.h | 9 +++
>> arch/arm64/kvm/sys_regs.c | 137 ++++++++++++++++++++++++++++++++++++++-
>> 2 files changed, 145 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
>> index 12f9dd7..993a7db 100644
>> --- a/arch/arm64/include/asm/kvm_asm.h
>> +++ b/arch/arm64/include/asm/kvm_asm.h
>> @@ -93,6 +93,15 @@
>> #define c10_AMAIR0 (AMAIR_EL1 * 2) /* Aux Memory Attr Indirection Reg */
>> #define c10_AMAIR1 (c10_AMAIR0 + 1)/* Aux Memory Attr Indirection Reg */
>> #define c14_CNTKCTL (CNTKCTL_EL1 * 2) /* Timer Control Register (PL1) */
>> +
>> +#define cp14_DBGDSCRext (MDSCR_EL1 * 2)
>> +#define cp14_DBGBCR0 (DBGBCR0_EL1 * 2)
>> +#define cp14_DBGBVR0 (DBGBVR0_EL1 * 2)
>> +#define cp14_DBGBXVR0 (cp14_DBGBVR0 + 1)
>> +#define cp14_DBGWCR0 (DBGWCR0_EL1 * 2)
>> +#define cp14_DBGWVR0 (DBGWVR0_EL1 * 2)
>> +#define cp14_DBGDCCINT (MDCCINT_EL1 * 2)
>> +
>> #define NR_COPRO_REGS (NR_SYS_REGS * 2)
>>
>> #define ARM_EXCEPTION_IRQ 0
>> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
>> index 98d60d1..5960d5b 100644
>> --- a/arch/arm64/kvm/sys_regs.c
>> +++ b/arch/arm64/kvm/sys_regs.c
>> @@ -474,12 +474,148 @@ static const struct sys_reg_desc sys_reg_descs[] = {
>> NULL, reset_val, FPEXC32_EL2, 0x70 },
>> };
>>
>> +static bool trap_dbgidr(struct kvm_vcpu *vcpu,
>> + const struct sys_reg_params *p,
>> + const struct sys_reg_desc *r)
>> +{
>> + if (p->is_write) {
>> + return ignore_write(vcpu, p);
>> + } else {
>> + u64 dfr = read_cpuid(ID_AA64DFR0_EL1);
>> + u64 pfr = read_cpuid(ID_AA64PFR0_EL1);
>> + u32 el3 = !!((pfr >> 12) & 0xf);
>> +
>> + *vcpu_reg(vcpu, p->Rt) = ((((dfr >> 20) & 0xf) << 28) |
>> + (((dfr >> 12) & 0xf) << 24) |
>> + (((dfr >> 28) & 0xf) << 20) |
>> + (6 << 16) | (el3 << 14) | (el3 << 12));
>> + return true;
>> + }
>> +}
>> +
>> +static bool trap_debug32(struct kvm_vcpu *vcpu,
>> + const struct sys_reg_params *p,
>> + const struct sys_reg_desc *r)
>> +{
>> + if (p->is_write) {
>> + vcpu_cp14(vcpu, r->reg) = *vcpu_reg(vcpu, p->Rt);
>> + vcpu->arch.debug_flags |= KVM_ARM64_DEBUG_DIRTY;
>> + } else {
>> + *vcpu_reg(vcpu, p->Rt) = vcpu_cp14(vcpu, r->reg);
>> + }
>> +
>> + return true;
>> +}
>> +
>> +#define DBG_BCR_BVR_WCR_WVR(n) \
>> + /* DBGBCRn */ \
>> + { Op1( 0), CRn( 0), CRm((n)), Op2( 4), trap_debug32, \
>> + NULL, (cp14_DBGBCR0 + (n) * 2) }, \
>> + /* DBGBVRn */ \
>> + { Op1( 0), CRn( 0), CRm((n)), Op2( 5), trap_debug32, \
>> + NULL, (cp14_DBGBVR0 + (n) * 2) }, \
>
> I think you switched the order of DBGBCRn and DBGBVRn here? Opc2==4 is
> the DBGBVR and Opc2==5 is the DBGBCR0.

I can't get it right, can I? It's amazing that it worked...

>> + /* DBGWVRn */ \
>> + { Op1( 0), CRn( 0), CRm((n)), Op2( 6), trap_debug32, \
>> + NULL, (cp14_DBGWVR0 + (n) * 2) }, \
>> + /* DBGWCRn */ \
>> + { Op1( 0), CRn( 0), CRm((n)), Op2( 7), trap_debug32, \
>> + NULL, (cp14_DBGWCR0 + (n) * 2) }
>> +
>> +#define DBGBXVR(n) \
>> + { Op1( 0), CRn( 1), CRm((n)), Op2( 1), trap_debug32, \
>> + NULL, cp14_DBGBXVR0 + n * 2 }
>> +
>> /* Trapped cp14 registers */
>> static const struct sys_reg_desc cp14_regs[] = {
>> + /* DBGIDR */
>> + { Op1( 0), CRn( 0), CRm( 0), Op2( 0), trap_dbgidr },
>> + /* DBGDTRRXext */
>> + { Op1( 0), CRn( 0), CRm( 0), Op2( 2), trap_raz_wi },
>> +
>> + DBG_BCR_BVR_WCR_WVR(0),
>> + /* DBGDSCRint */
>> + { Op1( 0), CRn( 0), CRm( 1), Op2( 0), trap_raz_wi },
>> + DBG_BCR_BVR_WCR_WVR(1),
>> + /* DBGDCCINT */
>> + { Op1( 0), CRn( 0), CRm( 2), Op2( 0), trap_debug32 },
>> + /* DBGDSCRext */
>> + { Op1( 0), CRn( 0), CRm( 2), Op2( 2), trap_debug32 },
>> + DBG_BCR_BVR_WCR_WVR(2),
>> + /* DBGDTRTXext */
>> + { Op1( 0), CRn( 0), CRm( 3), Op2( 2), trap_raz_wi },
>> + DBG_BCR_BVR_WCR_WVR(3),
>> + DBG_BCR_BVR_WCR_WVR(4),
>
> So we don't have a handler for the TRRX_int (nor the TRRX_EL0). I
> understand that it doesn't make sense to keep state for them or
> context-switch them, but do we never trap on these and if we do, is it
> then always valid to inject an undefined exception?

TRRXint has clearly been forgotten (Linux doesn't use it). TRRX_EL0 is
actually handled (see the comment that says DBGDTR[TR]X_EL0 in patch 3).

>> + DBG_BCR_BVR_WCR_WVR(5),
>> + /* DBGWFAR */
>> + { Op1( 0), CRn( 0), CRm( 6), Op2( 0), trap_raz_wi },
>> + /* DBGOSECCR */
>> + { Op1( 0), CRn( 0), CRm( 6), Op2( 2), trap_raz_wi },
>
> So it seems that we generally ignore everything related to external
> debug state, but we don't really document anywhere what our behavior is
> and what is and what is not supported towards the guest...

Happy to document that.

>> + DBG_BCR_BVR_WCR_WVR(6),
>> + /* DBGVCR */
>> + { Op1( 0), CRn( 0), CRm( 7), Op2( 0), trap_debug32 },
>> + DBG_BCR_BVR_WCR_WVR(7),
>> + DBG_BCR_BVR_WCR_WVR(8),
>> + DBG_BCR_BVR_WCR_WVR(9),
>> + DBG_BCR_BVR_WCR_WVR(10),
>> + DBG_BCR_BVR_WCR_WVR(11),
>> + DBG_BCR_BVR_WCR_WVR(12),
>> + DBG_BCR_BVR_WCR_WVR(13),
>> + DBG_BCR_BVR_WCR_WVR(14),
>> + DBG_BCR_BVR_WCR_WVR(15),
>> +
>> + /* DBGDRAR (32bit) */
>> + { Op1( 0), CRn( 1), CRm( 0), Op2( 0), trap_raz_wi },
>> +
>> + DBGBXVR(0),
>> + /* DBGOSLAR */
>> + { Op1( 0), CRn( 1), CRm( 0), Op2( 4), trap_raz_wi },
>> + DBGBXVR(1),
>> + /* DBGOSLSR */
>> + { Op1( 0), CRn( 1), CRm( 1), Op2( 4), trap_oslsr_el1 },
>> + DBGBXVR(2),
>> + DBGBXVR(3),
>> + /* DBGOSDLR */
>> + { Op1( 0), CRn( 1), CRm( 3), Op2( 4), trap_raz_wi },
>> + DBGBXVR(4),
>> + /* DBGPRCR */
>> + { Op1( 0), CRn( 1), CRm( 4), Op2( 4), trap_raz_wi },
>> + DBGBXVR(5),
>> + DBGBXVR(6),
>> + DBGBXVR(7),
>> + DBGBXVR(8),
>> + DBGBXVR(9),
>> + DBGBXVR(10),
>> + DBGBXVR(11),
>> + DBGBXVR(12),
>> + DBGBXVR(13),
>> + DBGBXVR(14),
>> + DBGBXVR(15),
>> +
>> + /* DBGDSAR (32bit) */
>> + { Op1( 0), CRn( 2), CRm( 0), Op2( 0), trap_raz_wi },
>> +
>
> we don't handle access to any implementation defined debug registers?
> Did we actually check what would be implemented for the cores we
> support?

No. So far, I've stuck with what the ARM ARM describe. Unless you're
thinking of a particular register I may ignored?

>> + /* DBGDEVID2 */
>> + { Op1( 0), CRn( 7), CRm( 0), Op2( 7), trap_raz_wi },
>> + /* DBGDEVID1 */
>> + { Op1( 0), CRn( 7), CRm( 1), Op2( 7), trap_raz_wi },
>> + /* DBGDEVID */
>> + { Op1( 0), CRn( 7), CRm( 2), Op2( 7), trap_raz_wi },
>> + /* DBGCLAIMSET */
>> + { Op1( 0), CRn( 7), CRm( 8), Op2( 6), trap_raz_wi },
>> + /* DBGCLAIMCLR */
>> + { Op1( 0), CRn( 7), CRm( 9), Op2( 6), trap_raz_wi },
>> +
>
> nit: why the sudden blank line?
>
>> + /* DBGAUTHSTATUS */
>> + { Op1( 0), CRn( 7), CRm(14), Op2( 6), trap_dbgauthstatus_el1 },
>> };
>>
>> /* Trapped cp14 64bit registers */
>> static const struct sys_reg_desc cp14_64_regs[] = {
>> + /* DBGDRAR (64bit) */
>> + { Op1( 0), CRm( 1), .access = trap_raz_wi },
>> +
>> + /* DBGDSAR (64bit) */
>> + { Op1( 0), CRm( 2), .access = trap_raz_wi },
>> };
>>
>> /*
>> @@ -527,7 +663,6 @@ static const struct sys_reg_desc cp15_regs[] = {
>> { Op1( 0), CRn(10), CRm( 3), Op2( 0), access_vm_reg, NULL, c10_AMAIR0 },
>> { Op1( 0), CRn(10), CRm( 3), Op2( 1), access_vm_reg, NULL, c10_AMAIR1 },
>> { Op1( 0), CRn(13), CRm( 0), Op2( 1), access_vm_reg, NULL, c13_CID },
>> -
>> };
>>
>> static const struct sys_reg_desc cp15_64_regs[] = {
>> --
>> 1.8.3.4
>>
>

--
Jazz is not dead. It just smells funny...