Messages in this thread | | | Date | Fri, 15 Jan 2021 18:30:16 +0100 | From | Jean-Philippe Brucker <> | Subject | Re: [PATCH v4 2/3] iommu/iova: Avoid double-negatives in magazine helpers |
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On Thu, Dec 10, 2020 at 02:23:08AM +0800, John Garry wrote: > A similar crash to the following could be observed if initial CPU rcache > magazine allocations fail in init_iova_rcaches():
Any idea why that's happening? This fix seems ok but if we're expecting allocation failures for the loaded magazine then we could easily get it for cpu_rcaches too, and get a similar abort at runtime.
Thanks, Jean
> Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000 > Mem abort info: > > free_iova_fast+0xfc/0x280 > iommu_dma_free_iova+0x64/0x70 > __iommu_dma_unmap+0x9c/0xf8 > iommu_dma_unmap_sg+0xa8/0xc8 > dma_unmap_sg_attrs+0x28/0x50 > cq_thread_v3_hw+0x2dc/0x528 > irq_thread_fn+0x2c/0xa0 > irq_thread+0x130/0x1e0 > kthread+0x154/0x158 > ret_from_fork+0x10/0x34 > > The issue is that expression !iova_magazine_full(NULL) evaluates true; this > falls over in __iova_rcache_insert() when we attempt to cache a mag and > cpu_rcache->loaded == NULL: > > if (!iova_magazine_full(cpu_rcache->loaded)) { > can_insert = true; > ... > > if (can_insert) > iova_magazine_push(cpu_rcache->loaded, iova_pfn); > > As above, can_insert is evaluated true, which it shouldn't be, and we try > to insert pfns in a NULL mag, which is not safe. > > To avoid this, stop using double-negatives, like !iova_magazine_full() and > !iova_magazine_empty(), and use positive tests, like > iova_magazine_has_space() and iova_magazine_has_pfns(), respectively; these > can safely deal with cpu_rcache->{loaded, prev} = NULL. > > Signed-off-by: John Garry <john.garry@huawei.com> > Tested-by: Xiang Chen <chenxiang66@hisilicon.com> > Reviewed-by: Zhen Lei <thunder.leizhen@huawei.com>
> --- > drivers/iommu/iova.c | 29 +++++++++++++++++------------ > 1 file changed, 17 insertions(+), 12 deletions(-) > > diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c > index cf1aacda2fe4..732ee687e0e2 100644 > --- a/drivers/iommu/iova.c > +++ b/drivers/iommu/iova.c > @@ -767,14 +767,18 @@ iova_magazine_free_pfns(struct iova_magazine *mag, struct iova_domain *iovad) > mag->size = 0; > } > > -static bool iova_magazine_full(struct iova_magazine *mag) > +static bool iova_magazine_has_space(struct iova_magazine *mag) > { > - return (mag && mag->size == IOVA_MAG_SIZE); > + if (!mag) > + return false; > + return mag->size < IOVA_MAG_SIZE; > } > > -static bool iova_magazine_empty(struct iova_magazine *mag) > +static bool iova_magazine_has_pfns(struct iova_magazine *mag) > { > - return (!mag || mag->size == 0); > + if (!mag) > + return false; > + return mag->size; > } > > static unsigned long iova_magazine_pop(struct iova_magazine *mag, > @@ -783,7 +787,7 @@ static unsigned long iova_magazine_pop(struct iova_magazine *mag, > int i; > unsigned long pfn; > > - BUG_ON(iova_magazine_empty(mag)); > + BUG_ON(!iova_magazine_has_pfns(mag)); > > /* Only fall back to the rbtree if we have no suitable pfns at all */ > for (i = mag->size - 1; mag->pfns[i] > limit_pfn; i--) > @@ -799,7 +803,7 @@ static unsigned long iova_magazine_pop(struct iova_magazine *mag, > > static void iova_magazine_push(struct iova_magazine *mag, unsigned long pfn) > { > - BUG_ON(iova_magazine_full(mag)); > + BUG_ON(!iova_magazine_has_space(mag)); > > mag->pfns[mag->size++] = pfn; > } > @@ -845,9 +849,9 @@ static bool __iova_rcache_insert(struct iova_domain *iovad, > cpu_rcache = raw_cpu_ptr(rcache->cpu_rcaches); > spin_lock_irqsave(&cpu_rcache->lock, flags); > > - if (!iova_magazine_full(cpu_rcache->loaded)) { > + if (iova_magazine_has_space(cpu_rcache->loaded)) { > can_insert = true; > - } else if (!iova_magazine_full(cpu_rcache->prev)) { > + } else if (iova_magazine_has_space(cpu_rcache->prev)) { > swap(cpu_rcache->prev, cpu_rcache->loaded); > can_insert = true; > } else { > @@ -856,8 +860,9 @@ static bool __iova_rcache_insert(struct iova_domain *iovad, > if (new_mag) { > spin_lock(&rcache->lock); > if (rcache->depot_size < MAX_GLOBAL_MAGS) { > - rcache->depot[rcache->depot_size++] = > - cpu_rcache->loaded; > + if (cpu_rcache->loaded) > + rcache->depot[rcache->depot_size++] = > + cpu_rcache->loaded; > } else { > mag_to_free = cpu_rcache->loaded; > } > @@ -908,9 +913,9 @@ static unsigned long __iova_rcache_get(struct iova_rcache *rcache, > cpu_rcache = raw_cpu_ptr(rcache->cpu_rcaches); > spin_lock_irqsave(&cpu_rcache->lock, flags); > > - if (!iova_magazine_empty(cpu_rcache->loaded)) { > + if (iova_magazine_has_pfns(cpu_rcache->loaded)) { > has_pfn = true; > - } else if (!iova_magazine_empty(cpu_rcache->prev)) { > + } else if (iova_magazine_has_pfns(cpu_rcache->prev)) { > swap(cpu_rcache->prev, cpu_rcache->loaded); > has_pfn = true; > } else { > -- > 2.26.2 > > _______________________________________________ > iommu mailing list > iommu@lists.linux-foundation.org > https://lists.linuxfoundation.org/mailman/listinfo/iommu
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