linux-kernel - Re: Broken pci_block_user_cfg

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Date:	Mon, 29 Aug 2011 19:23:05 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Jan Kiszka <jan.kiszka@...mens.com>
Cc:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Brian King <brking@...ibm.com>,
	"James E.J. Bottomley" <JBottomley@...allels.com>,
	"Hans J. Koch" <hjk@...sjkoch.de>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: Broken pci_block_user_cfg_access interface

On Mon, Aug 29, 2011 at 06:14:39PM +0200, Jan Kiszka wrote:
> On 2011-08-29 17:58, Michael S. Tsirkin wrote:
> > On Mon, Aug 29, 2011 at 05:42:16PM +0200, Jan Kiszka wrote:
> >> I still don't get what prevents converting ipr to allow plain mutex
> >> synchronization. My vision is:
> >>  - push reset-on-error of ipr into workqueue (or threaded IRQ?)
> >>  - require mutex synchronization for common config space access
> > 
> > Meaning pci_user_ read/write config?
> 
> And pci_dev_reset, yes.
> 
> > 
> >>     and the
> >>    full reset cycle
> >>  - only exception: INTx status/masking access
> >>     => use pci_lock + test for reset_in_progress, skip operation if
> >>        that is the case
> >>
> >> That would allow to drop the whole block_user_cfg infrastructure.
> >>
> >> Jan
> > 
> > We still need to block userspace access while INTx does
> > the status/masking access, right?
> 
> Yes, pci_lock would do that for us.

Well this means block_user_cfg is not going away,
this is what it really is: pci_lock + a bit to lock out userspace.

> We should consider making the related bits for INTx test & mask/unmask
> generic PCI services so that no user (uio_pci_generic, kvm, vfio) needs
> to worry about the locking details.
> 
> Jan
> 
> -- 
> Siemens AG, Corporate Technology, CT T DE IT 1
> Corporate Competence Center Embedded Linux
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