[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [PATCH v3 2/6] xen: pci: introduce reference counting for pdev
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Mon, 17 Apr 2023 12:51:26 +0200
- Arc-authentication-results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=citrix.com; dmarc=pass action=none header.from=citrix.com; dkim=pass header.d=citrix.com; arc=none
- Arc-message-signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector9901; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=luAQw0Nt9OFxoS6gBFVwZd4a0PvMp2HJZFmdmW97eas=; b=FdxtXebCNelXOgrEBW1GdAkgrGq8BU4YcQIHNgzWb3KED0JKEsr0ijKlLH0ZPgSNenPUowC3mLZ/xchsusMik3vhfy1EWYNmTw1ha4kpgjT5bZc2iFLqMRN1PT+GWdfpg4rEU/fD2bN0xHHiJL5CoksUQiIMOsS0fzKeTu9VWef08yCvFywkto38SuHRio9CJKaEk3oU5arbQ2kOD1yMc9dQUJzHJBP08m7NykwY9LAuaPr/kCVgOhl37RqwvOM5fn3tVAaJxq5ORwP4TlGVsDQZCwpmyzRpIpruQDuBh6yPGRhKsnEF9qznumNZorQcTMfNSuJHRGg4QRdmASl96Q==
- Arc-seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=I/hmmuG3r6ee95GWRggeUqiOWsuhW9JqyrDim/GSgVtoaFtYs66nEWPFOsDEhwCRsJsPykR4qv8SYEqqrmjVP+iiUcaivSZ9S8JC8hChFBDefaWWWmOvK6Pj0oqvF0ICreGAwZ8eyGfsh4luswfZMPmYTZK0t7PBIhV9UzF13OOQWEIZyYLBv7IIRMggpnVXnTnKqrzGsWcE5toKaOL72h6ivhWzC79Yi5WtCl5WDK7fg14cVejjYG8eR7VFhHJtlD4iW2XUibWPOr0F+yewHWUKhVh1tRldTnsJ1yc6X3Kxjor6UxB09HMUKhF2zu4hGcB/6MguUaOWhLPMkjTu5Q==
- Authentication-results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=citrix.com;
- Cc: Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Paul Durrant <paul@xxxxxxx>, Kevin Tian <kevin.tian@xxxxxxxxx>
- Delivery-date: Mon, 17 Apr 2023 10:51:53 +0000
- Ironport-data: A9a23:M5pk8KIKl658i/vWFE+RX5QlxSXFcZb7ZxGr2PjKsXjdYENShmdUn GMYUG2COfqLYWr0eYh0ad7j/BkFsJbSnYUwQQdlqX01Q3x08seUXt7xwmUcnc+xBpaaEB84t ZV2hv3odp1coqr0/0/1WlTZhSAgk/rOHvykU7Ss1hlZHWdMUD0mhQ9oh9k3i4tphcnRKw6Ws Jb5rta31GWNglaYCUpJrfPSwP9TlK6q4mhA4gVgPaojUGL2zBH5MrpOfcldEFOgKmVkNrbSb /rOyri/4lTY838FYj9yuu+mGqGiaue60Tmm0hK6aYD76vRxjnVaPpIAHOgdcS9qZwChxLid/ jnvWauYEm/FNoWU8AgUvoIx/ytWZcWq85efSZSzXFD6I+QrvBIAzt03ZHzaM7H09c40P3xl6 qIVKQxUMBPbi/7oz7OBVcRV05FLwMnDZOvzu1lG5BSAVLMMZ8CGRK/Ho9hFwD03m8ZCW+7EY NYUYiZuaxKGZABTPlAQC9Q1m+LAanvXKmUE7g7K4/dnpTGNnGSd05C0WDbRUsaNSshP2F6Ru 0rN/njjAwFcP9uaodaA2iv02LaezHyhCOr+EpXlx+dkrkDM4Vc9FS0UTHWwq+Cn0FGHDoc3x 0s8v3BGQbIJ3E6hQ8T5Xha4iGWZpRNaUN1Ve8UE7wWKxrvR8hyuLGEORT5ca/QrrMYzAzct0 zehj97vQDBirrCRYXac7auP6yO/PzAPKm0PbjNCShEKi/H8pKkjgxSJScxseIa3k9n0FDfY0 z2M6i8kiN07ltUX3q+2+VTGhTOEpZXTSAMxoALNUQqN9gpkYKa1aoru7kLUhd5DIZiYSB+dv XECs8mY8O0KS5qKkUSwrP4lGbio47OPNm3aiFs2Rp05rW3zqzikYJxa5yx4KAFxKMEYdDT1Y UjV/wRM+JtUO3jsZqhyC26sN/kXIWHbPYyNfpjpghBmOPCdqCfvEPlSWHOt
- Ironport-hdrordr: A9a23:uFikWK1UzVPmA5asNh5zDAqjBHYkLtp133Aq2lEZdPU0SKGlfq GV7ZEmPHrP4gr5N0tOpTntAse9qBDnhPxICOsqXYtKNTOO0AeVxelZhrcKqAeQeBEWmNQ96U 9hGZIOcuEZDzJB/LvHCN/TKadd/DGFmprY+ts31x1WPGVXgzkL1XYANu6ceHcGIzVuNN4CO7 e3wNFInDakcWR/VLXBOpFUN9KzweEijfjdEGc7OyI=
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Mon, Apr 17, 2023 at 12:34:31PM +0200, Jan Beulich wrote:
> On 17.04.2023 12:17, Roger Pau Monné wrote:
> > On Fri, Apr 14, 2023 at 01:30:39AM +0000, Volodymyr Babchuk wrote:
> >> Above I have proposed another view on this. I hope, it will work for
> >> you. Just to reiterate, idea is to allow "harmless" refcounts to be left
> >> after returning from pci_remove_device(). By "harmless" I mean that
> >> owners of those refcounts will not try to access the physical PCI
> >> device if pci_remove_device() is already finished.
> >
> > I'm not strictly a maintainer of this piece code, albeit I have an
> > opinion. I will like to also hear Jans opinion, since he is the
> > maintainer.
>
> I'm afraid I can't really appreciate the term "harmless refcounts". Whoever
> holds a ref is entitled to access the device. As stated before, I see only
> two ways of getting things consistent: Either pci_remove_device() is
> invoked upon dropping of the last ref,
With this approach, what would be the implementation of
PHYSDEVOP_manage_pci_remove? Would it just check whether the pdev
exist and either return 0 or -EBUSY?
> or it checks that it is dropping the
> last one. The former looks architecturally cleaner to me, but I can accept
> that moving there might be more of a change, so wouldn't object to going
> the latter route.
One of my concerns is what is expected of PHYSDEVOP_manage_pci_remove,
I don't think it's expected for PHYSDEVOP_manage_pci_remove to return
0 while there are users inside the hypervisor still holding a
reference to the pdev.
Thanks, Roger.
|
