On 2020/12/9 19:39, John Garry wrote: > On 09/12/2020 09:03, Leizhen (ThunderTown) wrote: >> >> >> On 2020/11/17 18:25, John Garry wrote: >>> A similar crash to the following could be observed if initial CPU rcache >>> magazine allocations fail in init_iova_rcaches(): >>> >>> Unable to handle kernel NULL pointer dereference at virtual address >>> 0000000000000000 >>> Mem abort info: >>> ESR = 0x96000004 >>> EC = 0x25: DABT (current EL), IL = 32 bits >>> SET = 0, FnV = 0 >>> EA = 0, S1PTW = 0 >>> Data abort info: >>> ISV = 0, ISS = 0x00000004 >>> CM = 0, WnR = 0 >>> [0000000000000000] user address but active_mm is swapper >>> Internal error: Oops: 96000004 [#1] PREEMPT SMP >>> Modules linked in: >>> CPU: 11 PID: 696 Comm: irq/40-hisi_sas Not tainted 5.9.0-rc7-dirty #109 >>> Hardware name: Huawei D06 /D06, BIOS Hisilicon D06 UEFI RC0 - V1.16.01 >>> 03/15/2019 >>> Call trace: >>> 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 >>> >>> Code: f9400060 f102001f 54000981 d4210000 (f9400043) >>> >>> ---[ end trace 4afcbdfc61b60467 ]--- >>> >>> The issue is that expression !iova_magazine_full(NULL) evaluates true; this >>> falls over in 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.ga...@huawei.com> > > Thanks for checking here... > >>> --- >>> 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 81b7399dd5e8..1f3f0f8b12e0 100644 >>> --- a/drivers/iommu/iova.c >>> +++ b/drivers/iommu/iova.c >>> @@ -827,14 +827,18 @@ 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, >>> @@ -843,7 +847,7 @@ 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--) >>> @@ -859,7 +863,7 @@ 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; >>> } >>> @@ -905,9 +909,9 @@ 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 { >>> @@ -916,8 +920,9 @@ 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) >> >> Looks like it just needs to change this place. Compiler ensures that >> mag->size >> will not be accessed when mag is NULL. > > Not sure about that. We would get a crash prior to touching this codepath: > > So if cpu_rcache->loaded == NULL at entry, then > !iova_magazine_full(cpu_rcache->loaded (==NULL) ) evaluates true, * above, so > can_insert is set true, and we then attempt > iova_magazine_push(cpu_rcache->loaded (==NULL), iova_pfn), which is not safe. > > ok?
OK, I got it. Reviewed-by: Zhen Lei <thunder.leiz...@huawei.com> > > Cheers, > John > >> >> static bool iova_magazine_full(struct iova_magazine *mag) >> { >> return (mag && mag->size == IOVA_MAG_SIZE); >> } >> >> static bool iova_magazine_empty(struct iova_magazine *mag) >> { >> return (!mag || mag->size == 0); >> } >> > > > > >> >>> + rcache->depot[rcache->depot_size++] = >>> + cpu_rcache->loaded; >>> } else { >>> mag_to_free = cpu_rcache->loaded; >>> } >>> @@ -968,9 +973,9 @@ 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 { >>> >> > > > . > _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu