Re: [Qemu-devel] [PATCH] pci: do not pci_update_mappings when guest gets bar size

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Oct 14, 2014 at 07:04:14PM +0800, arei.gonglei@huawei.com wrote:
> From: ChenLiang <chenliang88@huawei.com>
> 
> Power-up software can determine how much address space the device
> requires by writing a value of all 1's to the register and then
> reading the value back(PCI specification). Qemu should not do
> pci_update_mappings. Qemu may exit, because the wrong address of
> this bar is overlap with other memslots.
> 
> Signed-off-by: ChenLiang <chenliang88@huawei.com>
> Signed-off-by: Gonglei <arei.gonglei@huawei.com>

This is at best a work-around.
Overlapping is observed in practice, qemu really shouldn't exit when
this happens.
So we should find the root cause and fix it there instead of
adding work-arounds in PCI core.

With which device do you observe this?


> ---
>  hw/pci/pci.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> index 6ce75aa..4d44b44 100644
> --- a/hw/pci/pci.c
> +++ b/hw/pci/pci.c
> @@ -1158,12 +1158,12 @@ void pci_default_write_config(PCIDevice *d, uint32_t addr, uint32_t val_in, int
>          d->config[addr + i] = (d->config[addr + i] & ~wmask) | (val & wmask);
>          d->config[addr + i] &= ~(val & w1cmask); /* W1C: Write 1 to Clear */
>      }
> -    if (ranges_overlap(addr, l, PCI_BASE_ADDRESS_0, 24) ||
> +    if (((ranges_overlap(addr, l, PCI_BASE_ADDRESS_0, 24) ||
>          ranges_overlap(addr, l, PCI_ROM_ADDRESS, 4) ||
> -        ranges_overlap(addr, l, PCI_ROM_ADDRESS1, 4) ||
> -        range_covers_byte(addr, l, PCI_COMMAND))
> +        ranges_overlap(addr, l, PCI_ROM_ADDRESS1, 4)) &&
> +        val_in != 0xffffffff) || range_covers_byte(addr, l, PCI_COMMAND)) {
>          pci_update_mappings(d);
> -
> +    }
>      if (range_covers_byte(addr, l, PCI_COMMAND)) {
>          pci_update_irq_disabled(d, was_irq_disabled);
>          memory_region_set_enabled(&d->bus_master_enable_region,
> -- 
> 1.7.12.4
>