From eb3fa7cb51a2a35cd95eb92e65d8039c779468a5 Mon Sep 17 00:00:00 2001 From: "Keshavamurthy, Anil S" Date: Sun, 21 Oct 2007 16:41:52 -0700 Subject: [PATCH] Intel IOMMU: Avoid memory allocation failures in dma map api calls Intel IOMMU driver needs memory during DMA map calls to setup its internal page tables and for other data structures. As we all know that these DMA map calls are mostly called in the interrupt context or with the spinlock held by the upper level drivers(network/storage drivers), so in order to avoid any memory allocation failure due to low memory issues, this patch makes memory allocation by temporarily setting PF_MEMALLOC flags for the current task before making memory allocation calls. We evaluated mempools as a backup when kmem_cache_alloc() fails and found that mempools are really not useful here because 1) We don't know for sure how much to reserve in advance 2) And mempools are not useful for GFP_ATOMIC case (as we call memory alloc functions with GFP_ATOMIC) (akpm: point 2 is wrong...) With PF_MEMALLOC flag set in the current->flags, the VM subsystem avoids any watermark checks before allocating memory thus guarantee'ing the memory till the last free page. Further, looking at the code in mm/page_alloc.c in __alloc_pages() function, looks like this flag is useful only in the non-interrupt context. If we are in the interrupt context and memory allocation in IOMMU driver fails for some reason, then the DMA map api's will return failure and it is up to the higher level drivers to retry. Suppose, if upper level driver programs the controller with the buggy DMA virtual address, the IOMMU will block that DMA transaction when that happens thus preventing any corruption to main memory. So far in our test scenario, we were unable to create any memory allocation failure inside dma map api calls. Signed-off-by: Anil S Keshavamurthy Cc: Andi Kleen Cc: Peter Zijlstra Cc: Muli Ben-Yehuda Cc: "Siddha, Suresh B" Cc: Arjan van de Ven Cc: Ashok Raj Cc: "David S. Miller" Cc: Christoph Lameter Cc: Greg KH Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- drivers/pci/intel-iommu.c | 30 ++++++++++++++++++++++++++---- 1 file changed, 26 insertions(+), 4 deletions(-) diff --git a/drivers/pci/intel-iommu.c b/drivers/pci/intel-iommu.c index 93ed771b325..05630b44dbf 100644 --- a/drivers/pci/intel-iommu.c +++ b/drivers/pci/intel-iommu.c @@ -85,9 +85,31 @@ static struct kmem_cache *iommu_domain_cache; static struct kmem_cache *iommu_devinfo_cache; static struct kmem_cache *iommu_iova_cache; +static inline void *iommu_kmem_cache_alloc(struct kmem_cache *cachep) +{ + unsigned int flags; + void *vaddr; + + /* trying to avoid low memory issues */ + flags = current->flags & PF_MEMALLOC; + current->flags |= PF_MEMALLOC; + vaddr = kmem_cache_alloc(cachep, GFP_ATOMIC); + current->flags &= (~PF_MEMALLOC | flags); + return vaddr; +} + + static inline void *alloc_pgtable_page(void) { - return (void *)get_zeroed_page(GFP_ATOMIC); + unsigned int flags; + void *vaddr; + + /* trying to avoid low memory issues */ + flags = current->flags & PF_MEMALLOC; + current->flags |= PF_MEMALLOC; + vaddr = (void *)get_zeroed_page(GFP_ATOMIC); + current->flags &= (~PF_MEMALLOC | flags); + return vaddr; } static inline void free_pgtable_page(void *vaddr) @@ -97,7 +119,7 @@ static inline void free_pgtable_page(void *vaddr) static inline void *alloc_domain_mem(void) { - return kmem_cache_alloc(iommu_domain_cache, GFP_ATOMIC); + return iommu_kmem_cache_alloc(iommu_domain_cache); } static inline void free_domain_mem(void *vaddr) @@ -107,7 +129,7 @@ static inline void free_domain_mem(void *vaddr) static inline void * alloc_devinfo_mem(void) { - return kmem_cache_alloc(iommu_devinfo_cache, GFP_ATOMIC); + return iommu_kmem_cache_alloc(iommu_devinfo_cache); } static inline void free_devinfo_mem(void *vaddr) @@ -117,7 +139,7 @@ static inline void free_devinfo_mem(void *vaddr) struct iova *alloc_iova_mem(void) { - return kmem_cache_alloc(iommu_iova_cache, GFP_ATOMIC); + return iommu_kmem_cache_alloc(iommu_iova_cache); } void free_iova_mem(struct iova *iova) -- 2.20.1