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[2a00:1028:83b8:1e7a:3010:3bd6:8521:caf1]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-47d6be2ce32sm61878015e9.2.2026.01.05.05.40.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 05 Jan 2026 05:40:34 -0800 (PST) Date: Mon, 5 Jan 2026 14:40:31 +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: <20260105144031.2520c81b@mordecai> In-Reply-To: <20260105073621-mutt-send-email-mst@kernel.org> References: <0ffb3513d18614539c108b4548cdfbc64274a7d1.1767601130.git.mst@redhat.com> <20260105105433.5b875ce3@mordecai> <20260105073621-mutt-send-email-mst@kernel.org> X-Mailer: Claws Mail 4.3.1 (GTK 3.24.51; x86_64-suse-linux-gnu) Precedence: bulk X-Mailing-List: linux-crypto@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 07:37:31 -0500 "Michael S. Tsirkin" wrote: > On Mon, Jan 05, 2026 at 10:54:33AM +0100, Petr Tesarik wrote: > > 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 > > > I mean, yes it's not really required here, but the padding we had before > was broken (two spaces not aligning to anything). Oh, you're right! Yes, then let's fix it now, because you touch the neighbouring line. Sorry for the noise. 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, >