On 13.03.2025 18:48, Roger Pau Monné wrote:
> On Wed, Mar 12, 2025 at 03:50:17PM -0400, Stewart Hildebrand wrote:
>> @@ -585,10 +601,31 @@ static void cf_check bar_write(
>> {
>> /* If the value written is the current one avoid printing a
>> warning. */
>> if ( val != (uint32_t)(bar->addr >> (hi ? 32 : 0)) )
>> + {
>> gprintk(XENLOG_WARNING,
>> - "%pp: ignored BAR %zu write while mapped\n",
>> + "%pp: allowing BAR %zu write while mapped\n",
>> &pdev->sbdf, bar - pdev->vpci->header.bars + hi);
>
> If Xen now handles BARs writes with memory decoding enabled the
> message can be removed. It's only purpose was to signal this missing
> handling.
>
>> - return;
>> + ASSERT(rw_is_write_locked(&pdev->domain->pci_lock));
>> + ASSERT(spin_is_locked(&pdev->vpci->lock));
>> + reenable = true;
>> + cmd = pci_conf_read16(pdev->sbdf, PCI_COMMAND);
>> + /*
>> + * Write-while-mapped: unmap the old BAR in p2m. We want this to
>> + * finish right away since the deferral machinery only supports
>> + * unmap OR map, not unmap-then-remap. Ultimately, it probably
>> would
>> + * be better to defer the write-while-mapped case just like
>> regular
>> + * BAR writes (but still only allow it for 32-bit BAR writes).
>> + */
>> + /* Disable memory decoding */
>> + modify_bars(pdev, cmd & ~PCI_COMMAND_MEMORY, false);
>
> I think if the guest explicitly avoids toggling memory decoding Xen
> should also to the same, and not touch the bit.
For Dom0 I'm inclined to agree, but for DomU-s it may be unsafe to do so.
(You may have meant it like this, but you said "guest".)
Jan
