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c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1784099192; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=m0/Q/YYevEPHvKzDPJRAOvl85iWJCAk5Q7iHC3eSAQk=; b=KhOAhwEdBReGmhj+sM4OuHu5MeE4objjEeX3StdYsQKrUNtTffFzTmwtTJRSFEiK7h1EdQ Q0tv5P31GUDdNLTcuZAvj1S9nc2flnf/4aNWAbm6QnK4/2T/pwwmQKDeQBdFDL39Qf4Jv0 NsQEUC5/EYo3J82qOJ7ymp3zWKl47FI= X-MC-Unique: mECovYS_OwizZe0su7UWJA-1 X-Mimecast-MFC-AGG-ID: mECovYS_OwizZe0su7UWJA_1784099187 From: =?UTF-8?q?C=C3=A9dric=20Le=20Goater?= To: qemu-devel@nongnu.org Cc: Alex Williamson , =?UTF-8?q?C=C3=A9dric=20Le=20Goater?= , Nicolin Chen Subject: [PATCH] vfio/region: Clarify dma-buf failure messages Date: Wed, 15 Jul 2026 09:06:22 +0200 Message-ID: <20260715070622.198400-1-clg@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists1p.gnu.org; Received-SPF: permerror client-ip=170.10.133.124; envelope-from=clg@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 12 X-Spam_score: 1.2 X-Spam_bar: + X-Spam_report: (1.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, T_SPF_PERMERROR=0.01 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1784099235161158500 The dma-buf failure messages in vfio_region_create_dma_buf() say "PCI BAR IOMMU mappings may fail", which suggests the BAR is broken. In practice, only P2P DMA is affected -- normal passthrough uses the mmap fallback. Reword both messages to mention P2P DMA explicitly and clarify that the mmap fallback is in use. Use warn_report_err_once() at the call site so per-BAR repetition on mdev devices is suppressed. Fixes: dcf1b77e834d ("hw/vfio/region: Create dmabuf for PCI BAR per region") Cc: Nicolin Chen Signed-off-by: C=C3=A9dric Le Goater Reviewed-by: Philippe Mathieu-Daud=C3=A9 Reviewed-by: Rodolfo Vick --- hw/vfio/region.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) diff --git a/hw/vfio/region.c b/hw/vfio/region.c index dbde3391802691888ca31d5e329aba5ba680feb4..54ad11a6c8ed8e04fa365262ccb= 8bd694bdb45f7 100644 --- a/hw/vfio/region.c +++ b/hw/vfio/region.c @@ -321,13 +321,12 @@ static bool vfio_region_create_dma_buf(VFIORegion *re= gion, Error **errp) ret =3D vfio_device_get_feature(vbasedev, feature); if (ret < 0) { if (ret =3D=3D -ENOTTY) { - warn_report_once("VFIO dma-buf not supported in kernel: " - "PCI BAR IOMMU mappings may fail"); + warn_report_once("VFIO dma-buf not supported in kernel, " + "using mmap fallback, P2P DMA will not work"); return true; } - /* P2P DMA or exposing device memory use cases are not supported. = */ - error_setg_errno(errp, -ret, "%s: failed to create dma-buf: " - "PCI BAR IOMMU mappings may fail", + error_setg_errno(errp, -ret, "%s: dma-buf unavailable, " + "using mmap fallback, P2P DMA will not work", memory_region_name(region->mem)); return false; } @@ -448,7 +447,7 @@ int vfio_region_mmap(VFIORegion *region) } =20 if (!vfio_region_create_dma_buf(region, &local_err)) { - error_report_err(local_err); + warn_report_err_once(local_err); } =20 return 0; --=20 2.55.0