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[2a00:1028:83b8:1e7a:3010:3bd6:8521:caf1]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-47d6d452be4sm144233885e9.10.2026.01.05.01.54.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 05 Jan 2026 01:54:35 -0800 (PST) Date: Mon, 5 Jan 2026 10:54:33 +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 , Bartosz Golaszewski , 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 v2 05/15] dma-debug: track cache clean flag in entries Message-ID: <20260105105433.5b875ce3@mordecai> In-Reply-To: <0ffb3513d18614539c108b4548cdfbc64274a7d1.1767601130.git.mst@redhat.com> References: <0ffb3513d18614539c108b4548cdfbc64274a7d1.1767601130.git.mst@redhat.com> X-Mailer: Claws Mail 4.3.1 (GTK 3.24.51; x86_64-suse-linux-gnu) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 5 Jan 2026 03:23:10 -0500 "Michael S. Tsirkin" wrote: > If a driver is buggy 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. > > Signed-off-by: Michael S. Tsirkin > --- > kernel/dma/debug.c | 27 ++++++++++++++++++++++----- > 1 file changed, 22 insertions(+), 5 deletions(-) > > diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c > index 7e66d863d573..43d6a996d7a7 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; > + enum map_err_types map_err_type; *nitpick* unnecessary change in white space (breaks git-blame). Other than that, LGTM. I'm not formally a reviewer, but FWIW: Reviewed-by: Petr Tesarik Petr T > + 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 +492,16 @@ 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); > + /* A lookup failure here after we got -EEXIST is unexpected. */ > + WARN_ON(!existing); > + if (existing) > + *overlap_cache_clean = existing->is_cache_clean; > + } > spin_unlock_irqrestore(&radix_lock, flags); > > return rc; > @@ -583,20 +596,24 @@ 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,