On 19 September 2015 at 07:15, Edgar E. Iglesias
<[email protected]> wrote:
> From: "Edgar E. Iglesias" <[email protected]>
>
> The starting level for S2 pagetable walks is computed
> differently from the S1 starting level. Implement the S2
> variant.
>
> Signed-off-by: Edgar E. Iglesias <[email protected]>
> ---
> target-arm/helper.c | 32 ++++++++++++++++++++------------
> 1 file changed, 20 insertions(+), 12 deletions(-)
>
> diff --git a/target-arm/helper.c b/target-arm/helper.c
> index b709582..33be8c2 100644
> --- a/target-arm/helper.c
> +++ b/target-arm/helper.c
> @@ -6542,18 +6542,26 @@ static bool get_phys_addr_lpae(CPUARMState *env,
> target_ulong address,
> goto do_fault;
> }
>
> - /* The starting level depends on the virtual address size (which can be
> - * up to 48 bits) and the translation granule size. It indicates the
> number
> - * of strides (granule_sz bits at a time) needed to consume the bits
> - * of the input address. In the pseudocode this is:
> - * level = 4 - RoundUp((inputsize - grainsize) / stride)
> - * where their 'inputsize' is our 'va_size - tsz', 'grainsize' is
> - * our 'granule_sz + 3' and 'stride' is our 'granule_sz'.
> - * Applying the usual "rounded up m/n is (m+n-1)/n" and simplifying:
> - * = 4 - (va_size - tsz - granule_sz - 3 + granule_sz - 1) /
> granule_sz
> - * = 4 - (va_size - tsz - 4) / granule_sz;
> - */
> - level = 4 - (va_size - tsz - 4) / granule_sz;
> + if (mmu_idx == ARMMMUIdx_S2NS) {
> + unsigned int startlevel = extract32(tcr->raw_tcr, 6, 2);
> + level = 3 - startlevel;
> + if (granule_sz == 9) {
> + level = 2 - startlevel;
> + }
I think this is right code-wise but we could make it read a little more
nicely: if you make the condition be "if (mmu_idx != ARMMUIdx_S2NS)" then
the common case comes first and its long comment works as a description
of what we're doing here. Then the else clause can just say
/* For stage 2 translations the starting level is specified by the
* VCTR_EL2.SL0 field (whose interpretation depends on the page size)
*/
I was pondering whether writing it as
if (granule_sz == 9) {
/* 4K pages */
level = 2 - startlevel;
} else {
/* 16K or 64K pages */
level = 3 - startlevel;
}
would be slightly better, but it's marginal. Do add a "4K pages"
comment in somewhere, though.
> + } else {
> + /* The starting level depends on the virtual address size (which can
> + * be up to 48 bits) and the translation granule size. It indicates
> + * the number of strides (granule_sz bits at a time) needed to
> + * consume the bits of the input address. In the pseudocode this is:
> + * level = 4 - RoundUp((inputsize - grainsize) / stride)
> + * where their 'inputsize' is our 'va_size - tsz', 'grainsize' is
> + * our 'granule_sz + 3' and 'stride' is our 'granule_sz'.
> + * Applying the usual "rounded up m/n is (m+n-1)/n" and simplifying:
> + * = 4 - (va_size - tsz - granule_sz - 3 + granule_sz - 1) /
> granule_sz
> + * = 4 - (va_size - tsz - 4) / granule_sz;
> + */
> + level = 4 - (va_size - tsz - 4) / granule_sz;
> + }
>
> /* Clear the vaddr bits which aren't part of the within-region address,
> * so that we don't have to special case things when calculating the
> --
> 1.9.1
>
thanks
-- PMM
