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[2a00:1028:83b8:1e7a:3010:3bd6:8521:caf1]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-47be3af6dbdsm314869295e9.19.2026.01.01.23.59.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Jan 2026 23:59:36 -0800 (PST) Date: Fri, 2 Jan 2026 08:59:33 +0100 From: Petr Tesarik To: "Michael S. Tsirkin" Cc: linux-kernel@vger.kernel.org, Cong Wang , Jonathan Corbet , Olivia Mackall , Herbert Xu , Jason Wang , Paolo Bonzini , Stefan Hajnoczi , Eugenio =?UTF-8?B?UMOpcmV6?= , "James E.J. Bottomley" , "Martin K. Petersen" , Gerd Hoffmann , Xuan Zhuo , Marek Szyprowski , Robin Murphy , Stefano Garzarella , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Leon Romanovsky , Jason Gunthorpe , linux-doc@vger.kernel.org, linux-crypto@vger.kernel.org, virtualization@lists.linux.dev, linux-scsi@vger.kernel.org, iommu@lists.linux.dev, kvm@vger.kernel.org, netdev@vger.kernel.org Subject: Re: [PATCH RFC 05/13] dma-debug: track cache clean flag in entries Message-ID: <20260102085933.2f78123b@mordecai> In-Reply-To: References: X-Mailer: Claws Mail 4.3.1 (GTK 3.24.51; x86_64-suse-linux-gnu) Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Tue, 30 Dec 2025 05:16:00 -0500 "Michael S. Tsirkin" wrote: > If a driver is bugy and has 2 overlapping mappings but only > sets cache clean flag on the 1st one of them, we warn. > But if it only does it for the 2nd one, we don't. > > Fix by tracking cache clean flag in the entry. > Shrink map_err_type to u8 to avoid bloating up the struct. > > Signed-off-by: Michael S. Tsirkin > --- > kernel/dma/debug.c | 25 ++++++++++++++++++++----- > 1 file changed, 20 insertions(+), 5 deletions(-) > > diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c > index 7e66d863d573..9bd14fd4c51b 100644 > --- a/kernel/dma/debug.c > +++ b/kernel/dma/debug.c > @@ -63,6 +63,7 @@ enum map_err_types { > * @sg_mapped_ents: 'mapped_ents' from dma_map_sg > * @paddr: physical start address of the mapping > * @map_err_type: track whether dma_mapping_error() was checked > + * @is_cache_clean: driver promises not to write to buffer while mapped > * @stack_len: number of backtrace entries in @stack_entries > * @stack_entries: stack of backtrace history > */ > @@ -76,7 +77,8 @@ struct dma_debug_entry { > int sg_call_ents; > int sg_mapped_ents; > phys_addr_t paddr; > - enum map_err_types map_err_type; > + u8 map_err_type; Where exactly is the bloat? With my configuration, the size of struct dma_debug_entry is 128 bytes, with enough padding bytes at the end to keep it at 128 even if I keep this member an enum... Anyway, if there is a reason to keep this member small, I prefer to pack enum map_err_types instead: @@ -46,9 +46,9 @@ enum { enum map_err_types { MAP_ERR_CHECK_NOT_APPLICABLE, MAP_ERR_NOT_CHECKED, MAP_ERR_CHECKED, -}; +} __packed; #define DMA_DEBUG_STACKTRACE_ENTRIES 5 /** This will shrink it to a single byte but it will also keep the type information. > + bool is_cache_clean; > #ifdef CONFIG_STACKTRACE > unsigned int stack_len; > unsigned long stack_entries[DMA_DEBUG_STACKTRACE_ENTRIES]; > @@ -472,12 +474,15 @@ static int active_cacheline_dec_overlap(phys_addr_t cln) > return active_cacheline_set_overlap(cln, --overlap); > } > > -static int active_cacheline_insert(struct dma_debug_entry *entry) > +static int active_cacheline_insert(struct dma_debug_entry *entry, > + bool *overlap_cache_clean) > { > phys_addr_t cln = to_cacheline_number(entry); > unsigned long flags; > int rc; > > + *overlap_cache_clean = false; > + > /* If the device is not writing memory then we don't have any > * concerns about the cpu consuming stale data. This mitigates > * legitimate usages of overlapping mappings. > @@ -487,8 +492,14 @@ static int active_cacheline_insert(struct dma_debug_entry *entry) > > spin_lock_irqsave(&radix_lock, flags); > rc = radix_tree_insert(&dma_active_cacheline, cln, entry); > - if (rc == -EEXIST) > + if (rc == -EEXIST) { > + struct dma_debug_entry *existing; > + > active_cacheline_inc_overlap(cln); > + existing = radix_tree_lookup(&dma_active_cacheline, cln); > + if (existing) > + *overlap_cache_clean = existing->is_cache_clean; *nitpick* IIUC radix_tree_insert() returns -EEXIST only if the key is already present in the tree. Since radix_lock is not released between the insert attempt and this lookup, I don't see how this lookup could possibly fail. If it's not expected to fail, I would add a WARN_ON(). Please, do correct me if I'm missing something. Other than that, LGTM. Petr T > + } > spin_unlock_irqrestore(&radix_lock, flags); > > return rc; > @@ -583,20 +594,24 @@ DEFINE_SHOW_ATTRIBUTE(dump); > */ > static void add_dma_entry(struct dma_debug_entry *entry, unsigned long attrs) > { > + bool overlap_cache_clean; > struct hash_bucket *bucket; > unsigned long flags; > int rc; > > + entry->is_cache_clean = !!(attrs & DMA_ATTR_CPU_CACHE_CLEAN); > + > bucket = get_hash_bucket(entry, &flags); > hash_bucket_add(bucket, entry); > put_hash_bucket(bucket, flags); > > - rc = active_cacheline_insert(entry); > + rc = active_cacheline_insert(entry, &overlap_cache_clean); > if (rc == -ENOMEM) { > pr_err_once("cacheline tracking ENOMEM, dma-debug disabled\n"); > global_disable = true; > } else if (rc == -EEXIST && > - !(attrs & (DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_CPU_CACHE_CLEAN)) && > + !(attrs & DMA_ATTR_SKIP_CPU_SYNC) && > + !(entry->is_cache_clean && overlap_cache_clean) && > !(IS_ENABLED(CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC) && > is_swiotlb_active(entry->dev))) { > err_printk(entry->dev, entry,