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[80.230.31.118]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4324eab257asm84882883f8f.38.2026.01.02.03.17.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 02 Jan 2026 03:17:31 -0800 (PST) Date: Fri, 2 Jan 2026 06:17:28 -0500 From: "Michael S. Tsirkin" To: Petr Tesarik Cc: linux-kernel@vger.kernel.org, Cong Wang , Jonathan Corbet , Olivia Mackall , Herbert Xu , Jason Wang , Paolo Bonzini , Stefan Hajnoczi , Eugenio =?iso-8859-1?Q?P=E9rez?= , "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: <20260102060336-mutt-send-email-mst@kernel.org> References: <20260102085933.2f78123b@mordecai> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260102085933.2f78123b@mordecai> On Fri, Jan 02, 2026 at 08:59:33AM +0100, Petr Tesarik wrote: > 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... Ah, I missed ____cacheline_aligned_in_smp. Fixed. > > 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; Wow I didn't realize __packed can apply to enums. > #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 Sure, thanks! > > + } > > 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,