Re: [PATCH v9 04/16] iommu/exynos: allocate lv2 page table from own slab

Tomasz Figa
2013-08-09T09:35:33Z

On Friday 09 of August 2013 17:51:56 Cho KyongHo wrote:
> On Fri, 09 Aug 2013 09:55:30 +0200, Tomasz Figa wrote:
> > Hi KyongHo,
> >
> > On Friday 09 of August 2013 14:58:49 Cho KyongHo wrote:
> > > On Thu, 08 Aug 2013 16:00:18 +0200, Tomasz Figa wrote:
> > > > On Thursday 08 of August 2013 18:38:04 Cho KyongHo wrote:
> > > > > Since kmalloc() does not guarantee that the allignment of 1KiB
> > > > > when
> > > > > it
> > > > > allocates 1KiB, it is required to allocate lv2 page table from
> > > > > own
> > > > > slab that guarantees alignment of 1KiB
> > > > >
> > > > > Signed-off-by: Cho KyongHo <pullip.cho@samsung.com>
> > > > > ---
> > > > >
> > > > > drivers/iommu/exynos-iommu.c | 24 ++++++++++++++++++++----
> > > > > 1 files changed, 20 insertions(+), 4 deletions(-)
> > > > >
> > > > > diff --git a/drivers/iommu/exynos-iommu.c
> > > > > b/drivers/iommu/exynos-iommu.c index d90e6fa..a318049 100644
> > > > > --- a/drivers/iommu/exynos-iommu.c
> > > > > +++ b/drivers/iommu/exynos-iommu.c
> > > > > @@ -100,6 +100,8 @@
> > > > >
> > > > > #define REG_PB1_SADDR 0x054
> > > > > #define REG_PB1_EADDR 0x058
> > > > >
> > > > > +static struct kmem_cache *lv2table_kmem_cache;
> > > > > +
> > > > >
> > > > > static unsigned long *section_entry(unsigned long *pgtable,
> > > > > unsigned
> > > > >
> > > > > long iova) {
> > > > >
> > > > > return pgtable + lv1ent_offset(iova);
> > > > >
> > > > > @@ -765,7 +767,8 @@ static void
> > > > > exynos_iommu_domain_destroy(struct
> > > > > iommu_domain *domain)
> > > > >
> > > > > for (i = 0; i < NUM_LV1ENTRIES; i++)
> > > > >
> > > > > if (lv1ent_page(priv->pgtable + i))
> > > > >
> > > > > - kfree(__va(lv2table_base(priv->pgtable + i)));
> > > > > + kmem_cache_free(lv2table_kmem_cache,
> > > > > + __va(lv2table_base(priv->pgtable +
> >
> > i)));
> >
> > > > > free_pages((unsigned long)priv->pgtable, 2);
> > > > > free_pages((unsigned long)priv->lv2entcnt, 1);
> > > > >
> > > > > @@ -861,7 +864,7 @@ static unsigned long *alloc_lv2entry(unsigned
> > > > > long
> > > > > *sent, unsigned long iova, if (lv1ent_fault(sent)) {
> > > > >
> > > > > unsigned long *pent;
> > > > >
> > > > > - pent = kzalloc(LV2TABLE_SIZE, GFP_ATOMIC);
> > > > > + pent = kmem_cache_zalloc(lv2table_kmem_cache, GFP_ATOMIC);
> > > > >
> > > > > BUG_ON((unsigned long)pent & (LV2TABLE_SIZE - 1));
> > > > > if (!pent)
> > > > >
> > > > > return ERR_PTR(-ENOMEM);
> > > > >
> > > > > @@ -881,7 +884,7 @@ static int lv1set_section(unsigned long
> > > > > *sent,
> > > > > phys_addr_t paddr, short *pgcnt)
> > > > >
> > > > > if (lv1ent_page(sent)) {
> > > > >
> > > > > BUG_ON(*pgcnt != NUM_LV2ENTRIES);
> > > > >
> > > > > - kfree(page_entry(sent, 0));
> > > > > + kmem_cache_free(lv2table_kmem_cache, page_entry(sent, 0));
> > > > >
> > > > > *pgcnt = 0;
> > > > >
> > > > > }
> > > > >
> > > > > @@ -1082,10 +1085,23 @@ static int __init exynos_iommu_init(void)
> > > > >
> > > > > {
> > > > >
> > > > > int ret;
> > > > >
> > > > > + lv2table_kmem_cache =
> > > > > kmem_cache_create("exynos-iommu-lv2table",
> > > > > + LV2TABLE_SIZE, LV2TABLE_SIZE, 0, NULL);
> > > > > + if (!lv2table_kmem_cache) {
> > > > > + pr_err("%s: Failed to create kmem cache\n", __func__);
> > > > > + return -ENOMEM;
> > > > > + }
> > > > > +
> > > > >
> > > > > ret = platform_driver_register(&exynos_sysmmu_driver);
> > > > >
> > > > > if (ret == 0)
> > > > >
> > > > > - bus_set_iommu(&platform_bus_type, &exynos_iommu_ops);
> > > > > + ret = bus_set_iommu(&platform_bus_type,
> >
> > &exynos_iommu_ops);
> >
> > > > > +
> > > > > + if (ret) {
> > > > > + pr_err("%s: Failed to register exynos-iommu driver.\n",
> > > > > + __func__);
> > > > > + kmem_cache_destroy(lv2table_kmem_cache);
> > > > > + }
> > > >
> > > > What about making the return value handling here cleaner? For
example:
> > > > lv2table_kmem_cache = kmem_cache_create("exynos-iommu-lv2table",
> > > >
> > > > LV2TABLE_SIZE, LV2TABLE_SIZE, 0, NULL);
> > > >
> > > > if (!lv2table_kmem_cache) {
> > > >
> > > > ...
> > > > return -ENOMEM;
> > > >
> > > > }
> > > >
> > > > ret = platform_driver_register(&exynos_sysmmu_driver);
> > > > if (ret) {
> > > >
> > > > ...
> > > > goto err_destroy_kmem_cache;
> > > >
> > > > }
> > > >
> > > > ret = bus_set_iommu(&platform_bus_type, &exynos_iommu_ops);
> > > > if (ret) {
> > > >
> > > > ...
> > > > goto err_platform_unregister;
> > > >
> > > > }
> > > >
> > > > return 0;
> > > >
> > > > err_platform_unregister:
> > > > ...
> > > >
> > > > err_destroy_kmem_cache:
> > > > ...
> > > > return ret;
> > > >
> > > > }
> > >
> > > Thank you for suggestion.
> > > I think you are worrying about missing the information who makes
> > > 'ret'
> > > non-zero.
> >
> > Oh, this is a valid point, but it was more a nitpick about the coding
> > style. Single path error handling (with goto) is widely used in the
> > kernel in cases when more than one thing has to be undone and so I
> > suggested this method of error handling here as well.
> >
> > > Ok. I will process it separately.
> >
> > Since this patch adds most of the error handling to this function, I
> > think it should be fine to do it as a part of this patch.
>
> I meant 'separately' that checking all return values each.
> I think it can be simpler without goto.
>
> There are just 2 cases to rollback previous changes in that function.

It might end up with less lines, but having roll back in single place is
more readable. That's why it's the preferred error handling way in Linux
kernel, if you have more than one action to undo on your error path.

Best regards,
Tomasz