From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 AA36527FD49; Thu, 19 Mar 2026 11:06:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773918374; cv=none; b=kK1ch+NnATpRSZjk5sviYJzB/pCDn9baAyeScLm8WqnwA3yPOERTMr149Og5ZoLXN0UgK4qu3oypjqlwj/PPe4FOJo5B1msmtbQQkuuHsvn8XBKVF/dUDGwcnGbX+QYim1/E2ltGSb+sTVYRwwCH8pV96CF3SKtHmRqco3t91z0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773918374; c=relaxed/simple; bh=HtOLA8NR+v9NMav1R6I8Ldubjqi2Fb/1QOf8g53m3XA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=kk2g3HS9ivIKSudCeZd8YGfD/9lN5hGX3tIpdjgaqBCE+HBWQpZMNN+GzJhm9Iol4Jv1O66DwYHunK8+T+tua5SNu3CABQ4J5Nu6DzGvKsxbWtSqPh2AazlQIjd4vLoT1H/Lo2Rjj1u2que83JN4q89kRboQPGj6NhDodDJ5Loc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=nYIOxc6w; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="nYIOxc6w" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7DF25C19424; Thu, 19 Mar 2026 11:06:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773918374; bh=HtOLA8NR+v9NMav1R6I8Ldubjqi2Fb/1QOf8g53m3XA=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=nYIOxc6wuiHE1KLRNEIwUIHqRwXsElreuD2+B/6jZqyN4aIdu++mi/L+ZFP6YNh+y pv+9HlQoSNWZvemE++l3/lT/zSOQ6Bjs+z+TIZoqLHOKA2ThjWNFHlbdE2i/d8NqxP OafAVmojZqm13lZf5wvFbnu6sW6rMpQvN4ByIusAhKnp6STr84kaBFllVhy2h7AhRL tm1/xs3SAa1biSxootVlvvXZhBab/8Li/SwuTUuFXbUQx9CLxKmn4yRcM6vQHeKKQP RyXvw7BxjLLaaSX6u+wTFEDg9v2n7laBP6u4p1xHO9Px9fx994oVeOEU4mq5xXY5rZ 3nEO3+uI7S4Pw== Message-ID: <1f370bc0-e547-478b-b60c-8a5c77e7eb2f@kernel.org> Date: Thu, 19 Mar 2026 20:06:09 +0900 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4] scsi: sas: skip opt_sectors when DMA reports no real optimization hint To: "Ionut Nechita (Wind River)" , linux-scsi@vger.kernel.org Cc: James.Bottomley@HansenPartnership.com, ahuang12@lenovo.com, axboe@kernel.dk, damien.lemoal@opensource.wdc.com, hch@lst.de, iommu@lists.linux.dev, ionut_n2001@yahoo.com, john.g.garry@oracle.com, kbusch@kernel.org, linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, m.szyprowski@samsung.com, martin.petersen@oracle.com, robin.murphy@arm.com, sagi@grimberg.me, stable@vger.kernel.org, sunlightlinux@gmail.com References: <20260319083954.21056-1-ionut.nechita@windriver.com> <20260319083954.21056-2-ionut.nechita@windriver.com> Content-Language: en-US From: Damien Le Moal Organization: Western Digital Research In-Reply-To: <20260319083954.21056-2-ionut.nechita@windriver.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 3/19/26 17:39, Ionut Nechita (Wind River) wrote: > From: Ionut Nechita > > sas_host_setup() unconditionally sets shost->opt_sectors from > dma_opt_mapping_size(). When the IOMMU is disabled or in passthrough > mode and no DMA ops provide an opt_mapping_size callback, > dma_opt_mapping_size() returns min(dma_max_mapping_size(), SIZE_MAX) > which equals dma_max_mapping_size() — a hard upper bound, not an > optimization hint. Please reduce the distribution list. This is now a scsi patch. Nothing to do with iommu or nvme. > > On a Dell PowerEdge R750 with mpt3sas (Broadcom SAS3816, FW 33.15.00.00) > and intel_iommu=off the following values are observed: > > dma_opt_mapping_size() = dma_max_mapping_size() (no real hint) > shost->max_sectors = 32767 > opt_sectors = min(32767, huge >> 9) = 32767 > optimal_io_size = 32767 << 9 = 16776704 > → round_down(16776704, 4096) = 16773120 > > The SAS disk (SAMSUNG MZILT800HBHQ0D3) do not report an > Optimal Transfer Length in VPD page B0,so sdkp->opt_xfer_blocks remains 0. > sd_revalidate_disk() then uses min_not_zero(0, opt_sectors) = opt_sectors, > propagating the bogus value into the block device's optimal_io_size > (visible as OPT-IO = 16773120 in lsblk --topology). > > mkfs.xfs picks up optimal_io_size and minimum_io_size and computes: > > swidth = 16773120 / 4096 = 4095 > sunit = 8192 / 4096 = 2 > > Since 4095 % 2 != 0, XFS rejects the geometry: > > SB stripe unit sanity check failed > > This makes it impossible to create XFS filesystems (e.g. for > /var/lib/docker) during system bootstrap. > > Fix this by introducing a sas_dma_opt_sectors() helper that only returns > a non-zero opt_sectors when dma_opt_mapping_size() is strictly less than > dma_max_mapping_size(), indicating a genuine DMA optimization constraint > from an IOMMU or DMA ops backend. The helper also rounds the value down > to a power of two so that filesystem geometry calculations always produce > clean results. When the two DMA values are equal, no backend provided a > real hint, so opt_sectors stays at 0 ("no preference"). > > A WARN_ONCE guards against dma_opt_mapping_size() returning a value > larger than dma_max_mapping_size(), which would indicate a driver bug. > The return value uses min_t(unsigned int, ...) to avoid any potential > overflow when shifting the size_t opt value down to sectors. > > Fixes: 4cbfca5f7750 ("scsi: scsi_transport_sas: cap shost opt_sectors according to DMA optimal limit") > Cc: stable@vger.kernel.org > Signed-off-by: Ionut Nechita > --- > drivers/scsi/scsi_transport_sas.c | 40 +++++++++++++++++++++++++++---- > 1 file changed, 36 insertions(+), 4 deletions(-) > > diff --git a/drivers/scsi/scsi_transport_sas.c b/drivers/scsi/scsi_transport_sas.c > index 12124f9d5ccd0..696627b6fe2c3 100644 > --- a/drivers/scsi/scsi_transport_sas.c > +++ b/drivers/scsi/scsi_transport_sas.c > @@ -27,6 +27,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -222,6 +223,38 @@ static int sas_bsg_initialize(struct Scsi_Host *shost, struct sas_rphy *rphy) > * SAS host attributes > */ > > +/** > + * sas_dma_opt_sectors - derive opt_sectors from DMA optimal mapping size > + * @dma_dev: device to query DMA parameters for > + * @max_sectors: upper bound from the host adapter > + * > + * When the DMA layer reports a genuine optimization constraint (i.e. > + * dma_opt_mapping_size() < dma_max_mapping_size()), convert it to a > + * sector count, round it down to a power of two so that filesystem > + * geometry calculations stay sane, and cap it at @max_sectors. > + * > + * When the two values are equal no backend provided a real hint and > + * the function returns 0 ("no preference"). > + */ > +static unsigned int sas_dma_opt_sectors(struct device *dma_dev, > + unsigned int max_sectors) > +{ > + size_t opt = dma_opt_mapping_size(dma_dev); > + size_t max = dma_max_mapping_size(dma_dev); > + > + if (WARN_ONCE(opt > max, > + "dma_opt_mapping_size (%zu) > dma_max_mapping_size (%zu)\n", > + opt, max)) > + return 0; > + > + if (opt == max) > + return 0; > + > + opt = rounddown_pow_of_two(opt); > + > + return min_t(unsigned int, opt >> SECTOR_SHIFT, max_sectors); > +} > + > static int sas_host_setup(struct transport_container *tc, struct device *dev, > struct device *cdev) > { > @@ -239,10 +272,9 @@ static int sas_host_setup(struct transport_container *tc, struct device *dev, > dev_printk(KERN_ERR, dev, "fail to a bsg device %d\n", > shost->host_no); > > - if (dma_dev->dma_mask) { > - shost->opt_sectors = min_t(unsigned int, shost->max_sectors, > - dma_opt_mapping_size(dma_dev) >> SECTOR_SHIFT); > - } > + if (dma_dev->dma_mask) > + shost->opt_sectors = > + sas_dma_opt_sectors(dma_dev, shost->max_sectors); > > return 0; > } -- Damien Le Moal Western Digital Research