Hi Robin,
Recently, I have read and learned the code related to io-pgtable-arm.c.
There
are two question on arm_lpae_install_table.
1、the first
static arm_lpae_iopte arm_lpae_install_table(arm_lpae_iopte *table,
arm_lpae_iopte *ptep,
arm_lpae_iopte curr,
struct io_pgtable_cfg *cfg)
{
arm_lpae_iopte old, new;
new = __pa(table) | ARM_LPAE_PTE_TYPE_TABLE;
if (cfg->quirks & IO_PGTABLE_QUIRK_ARM_NS)
new |= ARM_LPAE_PTE_NSTABLE;
/*
* Ensure the table itself is visible before its PTE can be.
* Whilst we could get away with cmpxchg64_release below, this
* doesn't have any ordering semantics when !CONFIG_SMP.
*/
dma_wmb();
old = cmpxchg64_relaxed(ptep, curr, new);
if (cfg->coherent_walk || (old & ARM_LPAE_PTE_SW_SYNC))
return old;
/* Even if it's not ours, there's no point waiting; just kick
it */
__arm_lpae_sync_pte(ptep, cfg);
if (old == curr)
WRITE_ONCE(*ptep, new | ARM_LPAE_PTE_SW_SYNC);
return old;
}
If another thread changes the ptep between cmpxchg64_relaxed and
WRITE_ONCE(*ptep, new | ARM_LPAE_PTE_SW_SYNC), the operation
WRITE_ONCE will overwrite the change.
2、the second
for (i = 0; i < tablesz / sizeof(pte); i++, blk_paddr += split_sz) {
/* Unmap! */
if (i == unmap_idx)
continue;
__arm_lpae_init_pte(data, blk_paddr, pte, lvl,
&tablep[i]);
}
pte = arm_lpae_install_table(tablep, ptep, blk_pte, cfg);
When altering a translation table descriptor include split a block into
constituent granules, the Armv8-A and SMMUv3 architectures require
a break-before-make procedure. But in the function arm_lpae_split_blk_unmap,
it changes a block descriptor to an equivalent span of page translations
directly. Is it appropriate to do so?
The above two questions may be my wrong thinking. Coude you please
give me more hints?
Thanks,
Kunkun Jiang
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