Re: [PATCH v2 08/21] arm64: KVM: VHE: Introduce unified system register accessors

[Marc Zyngier]

On 01/02/16 13:47, Christoffer Dall wrote:
> On Mon, Jan 25, 2016 at 03:53:42PM +0000, Marc Zyngier wrote:
>> VHE brings its own bag of new system registers, or rather system
>> register accessors, as it define new ways to access both guest
>> and host system registers. For example, from the host:
>>
>> - The host TCR_EL2 register is accessed using the TCR_EL1 accessor
>> - The guest TCR_EL1 register is accessed using the TCR_EL12 accessor
>>
>> Obviously, this is confusing. A way to somehow reduce the complexity
>> of writing code for both ARMv8 and ARMv8.1 is to use a set of unified
>> accessors that will generate the right sysreg, depending on the mode
>> the CPU is running in. For example:
>>
>> - read_sysreg_el1(tcr) will use TCR_EL1 on ARMv8, and TCR_EL12 on
>>   ARMv8.1 with VHE.
>> - read_sysreg_el2(tcr) will use TCR_EL2 on ARMv8, and TCR_EL1 on
>>   ARMv8.1 with VHE.
>>
>> We end up with three sets of accessors ({read,write}_sysreg_el[012])
>> that can be directly used from C code. We take this opportunity to
>> also add the definition for the new VHE sysregs.(
> 
> weird closing parenthesis.
> 
>>
>> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
>> ---
>>  arch/arm64/kvm/hyp/hyp.h | 72 ++++++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 72 insertions(+)
>>
>> diff --git a/arch/arm64/kvm/hyp/hyp.h b/arch/arm64/kvm/hyp/hyp.h
>> index fc502f3..744c919 100644
>> --- a/arch/arm64/kvm/hyp/hyp.h
>> +++ b/arch/arm64/kvm/hyp/hyp.h
>> @@ -48,6 +48,78 @@ static inline unsigned long __hyp_kern_va(unsigned long v)
>>  
>>  #define hyp_kern_va(v) (typeof(v))(__hyp_kern_va((unsigned long)(v)))
>>  
>> +#define read_sysreg_elx(r,nvh,vh)					\
>> +	({								\
>> +		u64 reg;						\
>> +		asm volatile(ALTERNATIVE("mrs %0, " __stringify(r##nvh),\
>> +					 "mrs_s %0, " __stringify(r##vh),\
>> +					 ARM64_HAS_VIRT_HOST_EXTN)	\
>> +			     : "=r" (reg));				\
>> +		reg;							\
>> +	})
>> +
>> +#define write_sysreg_elx(v,r,nvh,vh)					\
>> +	do {								\
>> +		u64 __val = (u64)(v);					\
>> +		asm volatile(ALTERNATIVE("msr " __stringify(r##nvh) ", %x0",\
>> +					 "msr_s " __stringify(r##vh) ", %x0",\
>> +					 ARM64_HAS_VIRT_HOST_EXTN)	\
>> +					 : : "rZ" (__val));		\
> 
> what is rZ ?
> (complete Google-fu failure misery)

This gives the assembler the opportunity to generate a XZR register
access if the value is zero. See:

https://gcc.gnu.org/onlinedocs/gcc/Machine-Constraints.html#Machine-Constraints

> 
>> +	} while (0)
>> +
>> +/*
>> + * Unified accessors for registers that have a different encoding
>> + * between VHE and non-VHE. They must be specified without their "ELx"
>> + * encoding.
>> + */
>> +#define read_sysreg_el2(r)						\
>> +	({								\
>> +		u64 reg;						\
>> +		asm volatile(ALTERNATIVE("mrs %0, " __stringify(r##_EL2),\
>> +					 "mrs %0, " __stringify(r##_EL1),\
>> +					 ARM64_HAS_VIRT_HOST_EXTN)	\
>> +			     : "=r" (reg));				\
>> +		reg;							\
>> +	})
>> +
>> +#define write_sysreg_el2(v,r)						\
>> +	do {								\
>> +		u64 __val = (u64)(v);					\
>> +		asm volatile(ALTERNATIVE("msr " __stringify(r##_EL2) ", %x0",\
>> +					 "msr " __stringify(r##_EL1) ", %x0",\
>> +					 ARM64_HAS_VIRT_HOST_EXTN)	\
>> +					 : : "rZ" (__val));		\
>> +	} while (0)
>> +
>> +#define read_sysreg_el0(r)	read_sysreg_elx(r, _EL0, _EL02)
>> +#define write_sysreg_el0(v,r)	write_sysreg_elx(v, r, _EL0, _EL02)
>> +#define read_sysreg_el1(r)	read_sysreg_elx(r, _EL1, _EL12)
>> +#define write_sysreg_el1(v,r)	write_sysreg_elx(v, r, _EL1, _EL12)
>> +
>> +/* The VHE specific system registers and their encoding */
>> +#define sctlr_EL12              sys_reg(3, 5, 1, 0, 0)
>> +#define cpacr_EL12              sys_reg(3, 5, 1, 0, 2)
>> +#define ttbr0_EL12              sys_reg(3, 5, 2, 0, 0)
>> +#define ttbr1_EL12              sys_reg(3, 5, 2, 0, 1)
>> +#define tcr_EL12                sys_reg(3, 5, 2, 0, 2)
>> +#define afsr0_EL12              sys_reg(3, 5, 5, 1, 0)
>> +#define afsr1_EL12              sys_reg(3, 5, 5, 1, 1)
>> +#define esr_EL12                sys_reg(3, 5, 5, 2, 0)
>> +#define far_EL12                sys_reg(3, 5, 6, 0, 0)
>> +#define mair_EL12               sys_reg(3, 5, 10, 2, 0)
>> +#define amair_EL12              sys_reg(3, 5, 10, 3, 0)
>> +#define vbar_EL12               sys_reg(3, 5, 12, 0, 0)
>> +#define contextidr_EL12         sys_reg(3, 5, 13, 0, 1)
>> +#define cntkctl_EL12            sys_reg(3, 5, 14, 1, 0)
>> +#define cntp_tval_EL02          sys_reg(3, 5, 14, 2, 0)
>> +#define cntp_ctl_EL02           sys_reg(3, 5, 14, 2, 1)
>> +#define cntp_cval_EL02          sys_reg(3, 5, 14, 2, 2)
>> +#define cntv_tval_EL02          sys_reg(3, 5, 14, 3, 0)
>> +#define cntv_ctl_EL02           sys_reg(3, 5, 14, 3, 1)
>> +#define cntv_cval_EL02          sys_reg(3, 5, 14, 3, 2)
> 
> as always, fun stuff to review.

Well, short of having publicly available documentation, or force
everyone to upgrade their binutils to deal be able to cope with the new
sysregs, I don't know what else to do. I'm open to suggestions, though.

> 
>> +#define spsr_EL12               sys_reg(3, 5, 4, 0, 0)
>> +#define elr_EL12                sys_reg(3, 5, 4, 0, 1)
>> +
> 
> I couldn't quite decipher the spec as to how these are the right
> instruction encodings, so I'm going to trust the testing that this is
> done right.

If you have access to the spec, you have to play a substitution game
between the canonical encoding of the register accessed, and the
register used. For example:

SPSR_EL1 (3, 0, 4, 0, 0) -> SPSR_EL12 (3, 5, 4, 0, 0)

In practice, only Op1 changes.

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