Re: [XEN v2 10/11] xen/arm: Restrict zeroeth_table_offset for ARM_64

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 17 Jan 2023, Ayan Kumar Halder wrote:
> zeroeth_table_offset is not accessed by ARM_32.
> Also, when 32 bit physical addresses are used (ie ARM_PA_32=y), this
> causes an overflow.
> 
> Signed-off-by: Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>
> ---
> Changes from -
> 
> v1 - Removed the duplicate declaration for DECLARE_OFFSETS.
> 
>  xen/arch/arm/include/asm/lpae.h | 4 ++++
>  xen/arch/arm/mm.c               | 7 +------
>  2 files changed, 5 insertions(+), 6 deletions(-)
> 
> diff --git a/xen/arch/arm/include/asm/lpae.h b/xen/arch/arm/include/asm/lpae.h
> index 3fdd5d0de2..2744e0eebf 100644
> --- a/xen/arch/arm/include/asm/lpae.h
> +++ b/xen/arch/arm/include/asm/lpae.h
> @@ -259,7 +259,11 @@ lpae_t mfn_to_xen_entry(mfn_t mfn, unsigned int attr);
>  #define first_table_offset(va)  TABLE_OFFSET(first_linear_offset(va))
>  #define second_table_offset(va) TABLE_OFFSET(second_linear_offset(va))
>  #define third_table_offset(va)  TABLE_OFFSET(third_linear_offset(va))
> +#ifdef CONFIG_ARM_64

Julien was asking for a selectable Kconfig option that would allow us to
have 32-bit paddr_t even on ARM_64. If we do that, assuming we are on
aarch64, and we set VTCR_T0SZ to 0x20, hence we get 32-bit IPA, are we
going to have a 3-level or a 4-level p2m pagetable?

In any case I think this should be:
#ifndef CONFIG_PADDR_32

And if it doesn't work today on aarch64 due to pagetable levels or other
reasons, than I would make CONFIG_PADDR_32 not (yet) selectable on
ARM_64 (until it is fixed).


>  #define zeroeth_table_offset(va)  TABLE_OFFSET(zeroeth_linear_offset(va))
> +#else
> +#define zeroeth_table_offset(va)  0

Rather than 0 it might be better to have 32, hence zeroing the input
address


> +#endif
>  
>  /*
>   * Macros to define page-tables:
> diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
> index fab54618ab..95784e0c59 100644
> --- a/xen/arch/arm/mm.c
> +++ b/xen/arch/arm/mm.c
> @@ -207,12 +207,7 @@ void dump_pt_walk(paddr_t ttbr, paddr_t addr,
>  {
>      static const char *level_strs[4] = { "0TH", "1ST", "2ND", "3RD" };
>      const mfn_t root_mfn = maddr_to_mfn(ttbr);
> -    const unsigned int offsets[4] = {
> -        zeroeth_table_offset(addr),
> -        first_table_offset(addr),
> -        second_table_offset(addr),
> -        third_table_offset(addr)
> -    };
> +    DECLARE_OFFSETS(offsets, addr);
>      lpae_t pte, *mapping;
>      unsigned int level, root_table;
>  
> -- 
> 2.17.1
>