Re: [Xen-devel] [PATCH v4 1/5] vpci: fix updating the command register

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.11.18 at 15:32, <roger.pau@xxxxxxxxxx> wrote:
> On Fri, Nov 16, 2018 at 05:00:29AM -0700, Jan Beulich wrote:
>> >>> On 14.11.18 at 12:57, <roger.pau@xxxxxxxxxx> wrote:
>> > @@ -413,7 +412,7 @@ static void rom_write(const struct pci_dev *pdev, 
>> > unsigned int reg,
>> >          header->rom_enabled = new_enabled;
>> >          pci_conf_write32(pdev->seg, pdev->bus, slot, func, reg, val);
>> >      }
>> > -    else if ( modify_bars(pdev, new_enabled, true) )
>> > +    else if ( modify_bars(pdev, new_enabled ? PCI_COMMAND_MEMORY : 0, 
>> > true) )
>> 
>> Do you really mean to clear all other defined bits of the command
>> register here?
> 
> This is a ROM BAR write, not a command register write. rom_write
> passes PCI_COMMAND_MEMORY merely to signal this is a mapping
> operation, but the value would never be written to the command
> register, there's an ASSERT(!rom_only) just before the deferred write
> of the command register in modify_decoding.

Oh, I see. This is getting more subtle than it already was, so perhaps
worth attaching a brief comment here, the more that if anything was
wrong with the logic bad behavior would result in release builds?

Jan



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