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Re: [PATCH 8/9] vpci/header: Reset the command register when adding devices
- To: Oleksandr Andrushchenko <andr2000@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 6 Sep 2021 16:55:29 +0200
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- Cc: julien@xxxxxxx, sstabellini@xxxxxxxxxx, oleksandr_tyshchenko@xxxxxxxx, volodymyr_babchuk@xxxxxxxx, Artem_Mygaiev@xxxxxxxx, roger.pau@xxxxxxxxxx, bertrand.marquis@xxxxxxx, rahul.singh@xxxxxxx, Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Mon, 06 Sep 2021 14:55:39 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 03.09.2021 12:08, Oleksandr Andrushchenko wrote:
> --- a/xen/drivers/vpci/header.c
> +++ b/xen/drivers/vpci/header.c
> @@ -811,6 +811,16 @@ int vpci_bar_add_handlers(const struct domain *d, struct
> pci_dev *pdev)
> gprintk(XENLOG_ERR,
> "%pp: failed to add BAR handlers for dom%d\n", &pdev->sbdf,
> d->domain_id);
> +
> + /*
> + * Reset the command register: it is possible that when passing
> + * through a PCI device its memory decoding bits in the command
> + * register are already set. Thus, a guest OS may not write to the
> + * command register to update memory decoding, so guest mappings
> + * (guest's view of the BARs) are left not updated.
> + */
> + pci_conf_write16(pdev->sbdf, PCI_COMMAND, 0);
Can you really blindly write 0 here? What about bits that have to be
under host control, e.g. INTX_DISABLE? I can see that you may want to
hand off with I/O and memory decoding off and bus mastering disabled,
but for every other bit (including reserved ones) I'd expect separate
justification (in the commit message).
Jan
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