Re: [PATCH 9/9] xen/arm64: Remove READ/WRITE_SYSREG32 helper macros

[Julien Grall <julien@xxxxxxx>]

Hi Michal,

On 20/04/2021 08:08, Michal Orzel wrote:
> AArch64 system registers are 64bit whereas AArch32 ones
> are 32bit or 64bit. MSR/MRS are expecting 64bit values thus
> we should get rid of helpers READ/WRITE_SYSREG32
> in favour of using READ/WRITE_SYSREG.
> We should also use register_t type when reading sysregs
> which can correspond to uint64_t or uint32_t.
> Even though many AArch64 sysregs have upper 32bit reserved
> it does not mean that they can't be widen in the future.
As a general comment, all your commit message contains information about 
the goal (which is great). But they don't go much in details about the 
actual changes. I have tried to point out where I think those details 
would be helpful.
> As there are no other places in the code using READ/WRITE_SYSREG32,
> remove the helper macros.
>
> Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
> ---
>   xen/arch/arm/vcpreg.c               | 16 ++++++++++++++++
>   xen/include/asm-arm/arm64/sysregs.h |  5 -----
>   2 files changed, 16 insertions(+), 5 deletions(-)
>
> diff --git a/xen/arch/arm/vcpreg.c b/xen/arch/arm/vcpreg.c
> index c7f516ee0a..6cb7f3108c 100644
> --- a/xen/arch/arm/vcpreg.c
> +++ b/xen/arch/arm/vcpreg.c
> @@ -48,6 +48,7 @@
>    */
>   
>   /* The name is passed from the upper macro to workaround macro expansion. */
> +#ifdef CONFIG_ARM_32
>   #define TVM_REG(sz, func, reg...)                                           \
>   static bool func(struct cpu_user_regs *regs, uint##sz##_t *r, bool read)    \
>   {                                                                           \
> @@ -61,6 +62,21 @@ static bool func(struct cpu_user_regs *regs, uint##sz##_t 
> *r, bool read)    \
>                                                                               \
>       return true;                                                            \
>   }
> +#else /* CONFIG_ARM_64 */
> +#define TVM_REG(sz, func, reg...)                                           \
> +static bool func(struct cpu_user_regs *regs, uint##sz##_t *r, bool read)    \
> +{                                                                           \
> +    struct vcpu *v = current;                                               \
> +    bool cache_enabled = vcpu_has_cache_enabled(v);                         \
> +                                                                            \
> +    GUEST_BUG_ON(read);                                                     \
> +    WRITE_SYSREG(*r, reg);                                                  \
> +                                                                            \
> +    p2m_toggle_cache(v, cache_enabled);                                     \
> +                                                                            \
> +    return true;                                                            \
> +}
> +#endif
It would be nice if this change can be explained in the commit message. 
However, I think we can avoid the duplication by aliasing TVM_REG32() to 
TVM_REG64() on Arm64.
>   
>   #define TVM_REG32(regname, xreg) TVM_REG(32, vreg_emulate_##regname, xreg)
>   #define TVM_REG64(regname, xreg) TVM_REG(64, vreg_emulate_##regname, xreg)
> diff --git a/xen/include/asm-arm/arm64/sysregs.h 
> b/xen/include/asm-arm/arm64/sysregs.h
> index 077fd95fb7..83a1157ac4 100644
> --- a/xen/include/asm-arm/arm64/sysregs.h
> +++ b/xen/include/asm-arm/arm64/sysregs.h
> @@ -86,11 +86,6 @@
>   #endif
>   
>   /* Access to system registers */
> -
> -#define READ_SYSREG32(name) ((uint32_t)READ_SYSREG64(name))
> -
> -#define WRITE_SYSREG32(v, name) WRITE_SYSREG64((uint64_t)v, name)
> -
>   #define WRITE_SYSREG64(v, name) do {                    \
>       uint64_t _r = v;                                    \
>       asm volatile("msr "__stringify(name)", %0" : : "r" (_r));       \
Cheers,

--
Julien Grall