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Message-ID: <56AF65F7.5000404@arm.com>
Date: Mon, 1 Feb 2016 14:04:39 +0000
From: Marc Zyngier <marc.zyngier@....com>
To: Christoffer Dall <christoffer.dall@...aro.org>
Cc: Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
kvm@...r.kernel.org, kvmarm@...ts.cs.columbia.edu
Subject: Re: [PATCH v2 08/21] arm64: KVM: VHE: Introduce unified system
register accessors
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@....com>
>> ---
>> 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...
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