Re: [Qemu-devel] [PATCH v2 11/14] target-arm: Use correct memory attributes for page table walks

["Alex Bennée" <alex.bennee@linaro.org>]

Peter Maydell <peter.maydell@linaro.org> writes:

> Factor out the page table walk memory accesses into their own function,
> so that we can specify the correct S/NS memory attributes for them.
> This will also provide a place to use the correct endianness and
> handle the need for a stage-2 translation when virtualization is
> supported.
>
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
> ---
>  target-arm/helper.c | 49 ++++++++++++++++++++++++++++++++++++++++---------
>  1 file changed, 40 insertions(+), 9 deletions(-)
>
> diff --git a/target-arm/helper.c b/target-arm/helper.c
> index a568299..a01ff7f 100644
> --- a/target-arm/helper.c
> +++ b/target-arm/helper.c
> @@ -5129,6 +5129,29 @@ static bool get_level1_table_address(CPUARMState *env, ARMMMUIdx mmu_idx,
>      return true;
>  }
>  
> +/* All loads done in the course of a page table walk go through here.
> + * TODO: rather than ignoring errors from physical memory reads (which
> + * are external aborts in ARM terminology) we should propagate this
> + * error out so that we can turn it into a Data Abort if this walk
> + * was being done for a CPU load/store or an address translation instruction
> + * (but not if it was for a debug access).
> + */
> +static uint32_t arm_ldl_ptw(CPUState *cs, hwaddr addr, bool is_secure)
> +{
> +    MemTxAttrs attrs = {};
> +
> +    attrs.secure = is_secure;
> +    return address_space_ldl(cs->as, addr, attrs, NULL);
> +}
> +
> +static uint64_t arm_ldq_ptw(CPUState *cs, hwaddr addr, bool is_secure)
> +{
> +    MemTxAttrs attrs = {};
> +
> +    attrs.secure = is_secure;
> +    return address_space_ldq(cs->as, addr, attrs, NULL);
> +}
> +
>  static int get_phys_addr_v5(CPUARMState *env, uint32_t address, int access_type,
>                              ARMMMUIdx mmu_idx, hwaddr *phys_ptr,
>                              int *prot, target_ulong *page_size)
> @@ -5151,7 +5174,7 @@ static int get_phys_addr_v5(CPUARMState *env, uint32_t address, int access_type,
>          code = 5;
>          goto do_fault;
>      }
> -    desc = ldl_phys(cs->as, table);
> +    desc = arm_ldl_ptw(cs, table, regime_is_secure(env, mmu_idx));
>      type = (desc & 3);
>      domain = (desc >> 5) & 0x0f;
>      if (regime_el(env, mmu_idx) == 1) {
> @@ -5187,7 +5210,7 @@ static int get_phys_addr_v5(CPUARMState *env, uint32_t address, int access_type,
>              /* Fine pagetable.  */
>              table = (desc & 0xfffff000) | ((address >> 8) & 0xffc);
>          }
> -        desc = ldl_phys(cs->as, table);
> +        desc = arm_ldl_ptw(cs, table, regime_is_secure(env, mmu_idx));
>          switch (desc & 3) {
>          case 0: /* Page translation fault.  */
>              code = 7;
> @@ -5261,7 +5284,7 @@ static int get_phys_addr_v6(CPUARMState *env, uint32_t address, int access_type,
>          code = 5;
>          goto do_fault;
>      }
> -    desc = ldl_phys(cs->as, table);
> +    desc = arm_ldl_ptw(cs, table, regime_is_secure(env, mmu_idx));
>      type = (desc & 3);
>      if (type == 0 || (type == 3 && !arm_feature(env, ARM_FEATURE_PXN))) {
>          /* Section translation fault, or attempt to use the encoding
> @@ -5310,7 +5333,7 @@ static int get_phys_addr_v6(CPUARMState *env, uint32_t address, int access_type,
>          ns = extract32(desc, 3, 1);
>          /* Lookup l2 entry.  */
>          table = (desc & 0xfffffc00) | ((address >> 10) & 0x3fc);
> -        desc = ldl_phys(cs->as, table);
> +        desc = arm_ldl_ptw(cs, table, regime_is_secure(env, mmu_idx));
>          ap = ((desc >> 4) & 3) | ((desc >> 7) & 4);
>          switch (desc & 3) {
>          case 0: /* Page translation fault.  */
> @@ -5525,13 +5548,20 @@ static int get_phys_addr_lpae(CPUARMState *env, target_ulong address,
>      descaddr = extract64(ttbr, 0, 48);
>      descaddr &= ~((1ULL << (va_size - tsz - (granule_sz * (4 - level)))) - 1);
>  
> -    tableattrs = 0;
> +    /* Secure accesses start with the page table in secure memory and
> +     * can be downgraded to non-secure at any step. Non-secure accesses
> +     * remain non-secure. We implement this by just ORing in the NSTable/NS
> +     * bits at each step.
> +     */
> +    tableattrs = regime_is_secure(env, mmu_idx) ? 0 : (1 << 4);
<snip>

Again some new magic numbers added to the function but anyway:

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

>      /* Here descaddr is the final physical address, and attributes
> @@ -5705,8 +5735,9 @@ static inline int get_phys_addr(CPUARMState *env, target_ulong address,
>  {
>      if (mmu_idx == ARMMMUIdx_S12NSE0 || mmu_idx == ARMMMUIdx_S12NSE1) {
>          /* TODO: when we support EL2 we should here call ourselves recursively
> -         * to do the stage 1 and then stage 2 translations. The ldl_phys
> -         * calls for stage 1 will also need changing.
> +         * to do the stage 1 and then stage 2 translations. The arm_ld*_ptw
> +         * functions will also need changing to perform ARMMMUIdx_S2NS loads
> +         * rather than direct physical memory loads when appropriate.
>           * For non-EL2 CPUs a stage1+stage2 translation is just stage 1.
>           */
>          assert(!arm_feature(env, ARM_FEATURE_EL2));

-- 
Alex Bennée