From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C4BE533372B for ; Tue, 6 Jan 2026 14:51:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767711117; cv=none; b=kbPu0wpUMSe8IMHRlWq9H0Qe3SomwfM+pUJO989TIrA1pXTxX2ecKrVCm5q9ngdoRfvBAF1DErL9CiZ6xzBAJGHtQuP99Kmm6pBvt8njfQ65jbgVMMsbkgw16CzH4zRZQZZZ/oiDPg5kCpyS40WIOPg0d4Rvvht/v2Wo27AgLc8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767711117; c=relaxed/simple; bh=OtGN4S8+ZWGuAfn6+2YZp7eQlkz7c6TNLgozVUvUCR0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=aKAR4LwwBUKLGYKV6kmc7yf4B7Y8RhV+4se5th9vZKbffzuEpoyz4DiBkIYlutZwhZVfKb6+U+UW0hz6spmjShdn+9zb1MbfyhlYOBK6pkDDGWEH7YXtwrjc+e59uxahlWwrBk3BSzxJyqyXd29V3kkFDXLRelDj3Ah+2oYn2qg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=Fz+VC9XS; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b=FM0Ydb5f; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Fz+VC9XS"; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b="FM0Ydb5f" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1767711114; 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: in-reply-to:in-reply-to:references:references; bh=v8xGpc9e0AHSzqXJdY4dTy2UmvNhNHIufeUOIUm/LzQ=; b=Fz+VC9XSu90CRjcNJLIQR8xNtUCj1ZW9XBpV149bIDT3Qr89/Nk65oqEc5xrAecMOx92BB /eVHwbykvUmFSB34jwHAAn/uyuIlef66Ue5PPttGQ9H7uxgGnM+fWAImpDIr9g9yUZAcvM V8YPZK/Xk9Uqsfepli/BQQXn1xTY/Bc= Received: from mail-wr1-f70.google.com (mail-wr1-f70.google.com [209.85.221.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-612-3flPAkYgOOeQvvRWNPBN0g-1; Tue, 06 Jan 2026 09:51:53 -0500 X-MC-Unique: 3flPAkYgOOeQvvRWNPBN0g-1 X-Mimecast-MFC-AGG-ID: 3flPAkYgOOeQvvRWNPBN0g_1767711112 Received: by mail-wr1-f70.google.com with SMTP id ffacd0b85a97d-430f4609e80so488359f8f.3 for ; Tue, 06 Jan 2026 06:51:53 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=google; t=1767711112; x=1768315912; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=v8xGpc9e0AHSzqXJdY4dTy2UmvNhNHIufeUOIUm/LzQ=; b=FM0Ydb5fdan6x+pkR1pJDikE+5rPe3WwNvtNRo0JY14Evid+8FAayK9PXBBE19NE0V 6zmoqhY0DFOh8fYaTQ2w8a69KO0ECm6f9yz6/NSy6/VZS/jtDSpgR87LSsEQVtgtQI6C Bm4swC4PpZaaXSSi+1Oswc7hFfYQjX22ZoqFwC51cURGKJrO06ZoOhjZ5eZZRNVMGH/R j7RZUi/wX1uXswo38RIPdWsCg4iwKcSnQ4YDfJ6vEwh4pq+EaWgBUP7DDSaV301bGKCp 3WN9O3bTncPfs2vWtO7odr14bTSpvCTRf7UV8cA+BVh7m6Bzvi2UTfoEFMptn9FMl/Kb oPKw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1767711112; x=1768315912; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=v8xGpc9e0AHSzqXJdY4dTy2UmvNhNHIufeUOIUm/LzQ=; b=sVjVGz2sOa91eI9NzrdYNi12xmlRb8OVkrnBqKMhoB0NHviPEXbc51ir8QVHIjFOGL 5qkIghSuokRwCu4zeS97uSHo1xw7kV/pD+4jEUKY3P01WFaLy4babxOXXf1j9Sah3vnj 28ir1g95pPyt11MHI0IEtzNPAJ4SRdqzaeAuCtDF0QrJTgLo5NAoo/vv3X3lkgHoy6Ta bMqsvXE51hFDondxzuSZtSs1mkwx78CQbLkvVEu5Urjh8TwhXQslrgEbjyTyc8hnniGk zvzZIKqE+22XP3JSdzPZHFFso+m/Fwl+4j00ekjzauDdTr/X9gStiWe9zToxp2pLVtLv p1MA== X-Forwarded-Encrypted: i=1; AJvYcCUQuvkXo3RrRLD50lJObKrj0aYTghJ8fXya9ia7N4nZa1MausxbkyVLdKIs286PcHezwiFbthXYVAsD6EM=@vger.kernel.org X-Gm-Message-State: AOJu0Yy/a7uRMRQNJh8ShFvzfk8ss3TFDM7bS9W45zR7gzS0JtTDeYBN luhiTory6pWdKpTieKXBRr9xpV0Go70S9GgpzFz3h7dBwSv0GkZsGjfsmLY/eeBYqwrDVM1axCb sFQVGx0JEYYS+sR7TMcyHMSWO91NF/uJEnsYu97XsS75NAS4RkLvXPcsT92u6rKxgMg== X-Gm-Gg: AY/fxX7Fu80XXlLVqigEcVnYH6SXqsNsPULs2utkpHEouOiStG+morsDxGQDxUgYW7k 4CH6ArzLh1pgpQ5oaiACMtfPU93IC+JR6Vg40qBjIciSXHl83GEMqxuhza86azFNhDdrwENteFT JOU+7Qe5F0j9RMP3lsXnSNon8+2ahEGORXX3IIKcttHWJHvLKJQh8PQSHfns8RvZrDvUrRnmII9 CA/M9LVK1Q2Ak500/Vk6GP5VRrWvzZ6YjeLTvk7YxzZKfunOUHsDZ9OE7QGRVkrR50sTCFPKg64 A4oKv0gbrWipSxiUuDP4G/IGcNBVmlClzPJj4dd9RHJqgoMY31otuijOg+76xHSpCsWTQ+JbkOr FmT846A1qHU6pQHr7T3RokDJ4/GuzZP2ScQ== X-Received: by 2002:a05:6000:200f:b0:431:b6e:8be3 with SMTP id ffacd0b85a97d-432bc9f6dccmr4753185f8f.38.1767711112107; Tue, 06 Jan 2026 06:51:52 -0800 (PST) X-Google-Smtp-Source: AGHT+IGOynDA9QP29UwN/sUhG6OCzOdNXrD0Y6rHdaimQHcJZW2G3EKin+vfxrhBk6BDORYTgSmwkg== X-Received: by 2002:a05:6000:200f:b0:431:b6e:8be3 with SMTP id ffacd0b85a97d-432bc9f6dccmr4753140f8f.38.1767711111656; Tue, 06 Jan 2026 06:51:51 -0800 (PST) Received: from redhat.com (IGLD-80-230-31-118.inter.net.il. [80.230.31.118]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-432bd5ede7esm4752453f8f.32.2026.01.06.06.51.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 Jan 2026 06:51:51 -0800 (PST) Date: Tue, 6 Jan 2026 09:51:46 -0500 From: "Michael S. Tsirkin" To: Stefan Hajnoczi Cc: linux-kernel@vger.kernel.org, Cong Wang , Jonathan Corbet , Olivia Mackall , Herbert Xu , Jason Wang , Paolo Bonzini , 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 , Petr Tesarik , 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 10/15] virtio_scsi: fix DMA cacheline issues for events Message-ID: <20260106095044-mutt-send-email-mst@kernel.org> References: <8801aeef7576a155299f19b6887682dd3a272aba.1767601130.git.mst@redhat.com> <20260105181939.GA59391@fedora> 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-Disposition: inline In-Reply-To: <20260105181939.GA59391@fedora> On Mon, Jan 05, 2026 at 01:19:39PM -0500, Stefan Hajnoczi wrote: > On Mon, Jan 05, 2026 at 03:23:29AM -0500, Michael S. Tsirkin wrote: > > @@ -61,7 +62,7 @@ struct virtio_scsi_cmd { > > > > struct virtio_scsi_event_node { > > struct virtio_scsi *vscsi; > > - struct virtio_scsi_event event; > > + struct virtio_scsi_event *event; > > struct work_struct work; > > }; > > > > @@ -89,6 +90,11 @@ struct virtio_scsi { > > > > struct virtio_scsi_vq ctrl_vq; > > struct virtio_scsi_vq event_vq; > > + > > + __dma_from_device_group_begin(); > > + struct virtio_scsi_event events[VIRTIO_SCSI_EVENT_LEN]; > > + __dma_from_device_group_end(); > > If the device emits two events in rapid succession, could the CPU see > stale data for the second event because it already holds the cache line > for reading the first event? > > In other words, it's not obvious to me that the DMA warnings are indeed > spurious and should be silenced here. > > It seems safer and simpler to align and pad the struct virtio_scsi_event > field in struct virtio_scsi_event_node rather than packing these structs > into a single array here they might share cache lines. > > Stefan To add to what I wrote, that's a lot of overhead: 8 * 128 - about 1K on some platforms, and these happen to be low end ones. -- MST