linux-kernel - Re: [RFT][PATCH v2 3/9] vfio/ccw: Only pass in contiguous pages

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Wed, 6 Jul 2022 14:05:53 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Nicolin Chen <nicolinc@...dia.com>
Cc:     kwankhede@...dia.com, corbet@....net, hca@...ux.ibm.com,
        gor@...ux.ibm.com, agordeev@...ux.ibm.com,
        borntraeger@...ux.ibm.com, svens@...ux.ibm.com,
        zhenyuw@...ux.intel.com, zhi.a.wang@...el.com,
        jani.nikula@...ux.intel.com, joonas.lahtinen@...ux.intel.com,
        rodrigo.vivi@...el.com, tvrtko.ursulin@...ux.intel.com,
        airlied@...ux.ie, daniel@...ll.ch, farman@...ux.ibm.com,
        mjrosato@...ux.ibm.com, pasic@...ux.ibm.com, vneethv@...ux.ibm.com,
        oberpar@...ux.ibm.com, freude@...ux.ibm.com,
        akrowiak@...ux.ibm.com, jjherne@...ux.ibm.com,
        alex.williamson@...hat.com, cohuck@...hat.com,
        kevin.tian@...el.com, hch@...radead.org, jchrist@...ux.ibm.com,
        kvm@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        intel-gvt-dev@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org
Subject: Re: [RFT][PATCH v2 3/9] vfio/ccw: Only pass in contiguous pages

On Tue, Jul 05, 2022 at 11:27:53PM -0700, Nicolin Chen wrote:
> This driver is the only caller of vfio_pin/unpin_pages that might pass
> in a non-contiguous PFN list, but in many cases it has a contiguous PFN
> list to process. So letting VFIO API handle a non-contiguous PFN list
> is actually counterproductive.
> 
> Add a pair of simple loops to pass in contiguous PFNs only, to have an
> efficient implementation in VFIO.
> 
> Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> ---
>  drivers/s390/cio/vfio_ccw_cp.c | 70 +++++++++++++++++++++++++++-------
>  1 file changed, 56 insertions(+), 14 deletions(-)

I think this is fine as-is for this series, but someone who knows and
can test ccw should go in and fix things so that pfn_array_alloc()
doesn't exist. Allocating memory and filling it with consecutive
integers is kind of silly given we can just call vfio_pin_pages() with
pa_nr directly.

	pa->pa_iova_pfn[0] = pa->pa_iova >> PAGE_SHIFT;
	pa->pa_pfn[0] = -1ULL;
	for (i = 1; i < pa->pa_nr; i++) {
		pa->pa_iova_pfn[i] = pa->pa_iova_pfn[i - 1] + 1;

It looks like only the 'ccw_is_idal' flow can actually create
non-continuities. Also the loop in copy_from_iova() should ideally be
using the much faster 'rw' interface, and not a pin/unpin cycle just
to memcpy.

If I guess right these changes would significantly speed this driver
up.

Anyhow,

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason