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

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Nov 19, 2018 at 01:26:11AM -0700, Jan Beulich wrote:
> >>> 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?

It would, I could change the ASSERT to a BUG in modify_decoding if
that seems more foolproof.

Thanks, Roger.

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