Re: [PATCH 5/9] arm/mm: Get rid of READ/WRITE_SYSREG32

[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.
>
> Modify SCTLR_EL2 accesses to use READ/WRITE_SYSREG.
SCTLR_EL2 already has bits defined in the range [32:63]. So this change 
is going to have a side effect as AFAICT head.S will not touch those 
bits. So they are now going to be preserved.
The Arm Arm defines them as unknown if implemented. Therefore shouldn't 
we zero them somewhere else?
In any case, I think the commit message ought to contain an analysis for 
system registers that happened to have bits defined in the range [32:63].
> Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
> ---
>   xen/arch/arm/mm.c    | 2 +-
>   xen/arch/arm/traps.c | 2 +-
>   2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
> index 59f8a3f15f..0e07335291 100644
> --- a/xen/arch/arm/mm.c
> +++ b/xen/arch/arm/mm.c
> @@ -613,7 +613,7 @@ void __init remove_early_mappings(void)
>    */
>   static void xen_pt_enforce_wnx(void)
>   {
> -    WRITE_SYSREG32(READ_SYSREG32(SCTLR_EL2) | SCTLR_Axx_ELx_WXN, SCTLR_EL2);
> +    WRITE_SYSREG(READ_SYSREG(SCTLR_EL2) | SCTLR_Axx_ELx_WXN, SCTLR_EL2);
>       /*
>        * The TLBs may cache SCTLR_EL2.WXN. So ensure it is synchronized
>        * before flushing the TLBs.
> diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
> index c7acdb2087..e7384381cc 100644
> --- a/xen/arch/arm/traps.c
> +++ b/xen/arch/arm/traps.c
> @@ -915,7 +915,7 @@ static void _show_registers(const struct cpu_user_regs 
> *regs,
>       printk(" VTTBR_EL2: %016"PRIx64"\n", ctxt->vttbr_el2);
>       printk("\n");
>   
> -    printk(" SCTLR_EL2: %08"PRIx32"\n", READ_SYSREG32(SCTLR_EL2));
> +    printk(" SCTLR_EL2: %"PRIregister"\n", READ_SYSREG(SCTLR_EL2));
>       printk("   HCR_EL2: %"PRIregister"\n", READ_SYSREG(HCR_EL2));
>       printk(" TTBR0_EL2: %016"PRIx64"\n", READ_SYSREG64(TTBR0_EL2));
>       printk("\n");
Cheers,

--
Julien Grall