Re: [PATCH v2] xen/arm64: Remove READ/WRITE_SYSREG32 helper macros

[Julien Grall <julien@xxxxxxx>]

Hi Michal,

On 09/07/2021 13:40, 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.
>
> The last place in code making use of READ/WRITE_SYSREG32
> on arm64 is in TVM_REG macro defining functions vreg_emulate_<register>.
> Implement a macro WRITE_SYSREG_SZ which expands as follows:
> -on arm64: WRITE_SYSREG
> -on arm32: WRITE_SYSREG{32/64}
>
> As there are no other places in the code using these helpers
> on arm64 - remove them.
>
> Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
> ---
> Changes since v1:
> -implement WRITE_SYSREG_SZ instead of duplicating the TVM_REG
> ---
>   xen/arch/arm/vcpreg.c               | 12 +++++++++++-
>   xen/include/asm-arm/arm64/sysregs.h |  4 ----
>   2 files changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/xen/arch/arm/vcpreg.c b/xen/arch/arm/vcpreg.c
> index f0cdcc8a54..10c4846954 100644
> --- a/xen/arch/arm/vcpreg.c
> +++ b/xen/arch/arm/vcpreg.c
> @@ -47,6 +47,16 @@
>    *
>    */
>   
> +#ifdef CONFIG_ARM_64
> +#define WRITE_SYSREG_SZ(sz, val, sysreg)     WRITE_SYSREG(val, sysreg)
I think you want to cast to (uint##sz##_t) to avoid any surprise. I think...

> +#else
> +/*
> + * WRITE_SYSREG{32/64} on arm32 is defined as variadic macro which imposes
> + * on the below macro to be defined like that as well.
> + */
> +#define WRITE_SYSREG_SZ(sz, val, sysreg...)  WRITE_SYSREG##sz(val, sysreg)
> +#endif
> +
>   /* The name is passed from the upper macro to workaround macro expansion. */
>   #define TVM_REG(sz, func, reg...)                                           \
>   static bool func(struct cpu_user_regs *regs, uint##sz##_t *r, bool read)    \
> @@ -55,7 +65,7 @@ static bool func(struct cpu_user_regs *regs, uint##sz##_t *r, 
> bool read)    \
>       bool cache_enabled = vcpu_has_cache_enabled(v);                         \
>                                                                               \
>       GUEST_BUG_ON(read);                                                     \
> -    WRITE_SYSREG##sz(*r, reg);                                              \
> +    WRITE_SYSREG_SZ(sz, *r, reg);                                           \
>                                                                               \
>       p2m_toggle_cache(v, cache_enabled);                                     \
>                                                                               \
> diff --git a/xen/include/asm-arm/arm64/sysregs.h 
> b/xen/include/asm-arm/arm64/sysregs.h
> index 077fd95fb7..795901e1ba 100644
> --- a/xen/include/asm-arm/arm64/sysregs.h
> +++ b/xen/include/asm-arm/arm64/sysregs.h
> @@ -87,10 +87,6 @@
>   
>   /* Access to system registers */
>   
> -#define READ_SYSREG32(name) ((uint32_t)READ_SYSREG64(name))
> -
> -#define WRITE_SYSREG32(v, name) WRITE_SYSREG64((uint64_t)v, name)
... this was intended behavior but I used the wrong cast here.

> -
>   #define WRITE_SYSREG64(v, name) do {                    \
>       uint64_t _r = v;                                    \
>       asm volatile("msr "__stringify(name)", %0" : : "r" (_r));       \
--
Julien Grall