Re: [Qemu-devel] [PATCH 2/2] pcie_aer: clear cmask for Advanced Error Interrupt Message Number

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

On Fri, Aug 31, 2012 at 10:45:52AM -0400, Jason Baron wrote:
> On Fri, Aug 31, 2012 at 11:42:27AM +0300, Michael S. Tsirkin wrote:
> > Some minor nits below. If you dont get to it I will tweak this patch
> > when I apply it early next week.
> > 
> > On Thu, Aug 30, 2012 at 01:51:15PM -0400, Jason Baron wrote:
> > > The Advanced Error Interrupt Message Number (bits 31:27 of the Root
> > > Error Status Register) is updated when the number of msi messages assigned to a
> > > device changes. Migration of windows 7 on q35 chipset failed because the check
> > > in get_pci_config_device() fails due to wmask being set on these bits.
> > 
> > I think you actually mean 'not being set on these bits'?
> > 
> 
> No, the check is:
> 
> static int get_pci_config_device(QEMUFile *f, void *pv, size_t size)
> {
>     PCIDevice *s = container_of(pv, PCIDevice, config);
>     uint8_t *config;
>     int i;
> 
>     assert(size == pci_config_size(s));
>     config = g_malloc(size);
> 
>     qemu_get_buffer(f, config, size);
>     for (i = 0; i < size; ++i) {
>         if ((config[i] ^ s->config[i]) &
>             s->cmask[i] & ~s->wmask[i] & ~s->w1cmask[i]) {
>             g_free(config);
>             return -EINVAL;
>         }
>     }
> .....
> 
> So because cmask is set and these bits differ in config space (due to
> them being updated before migration), the migration aborts.

Ah so you mean 'cmask being set' - not wmask as you wrote.

> 
> > > Its valid
> > > to update these bits and we must restore this state across migration.
> > > 
> > > Signed-off-by: Jason Baron <jbaron@redhat.com>
> > > ---
> > >  hw/pcie_aer.c |    6 ++++++
> > >  1 files changed, 6 insertions(+), 0 deletions(-)
> > > 
> > > diff --git a/hw/pcie_aer.c b/hw/pcie_aer.c
> > > index 3b6981c..6edcd79 100644
> > > --- a/hw/pcie_aer.c
> > > +++ b/hw/pcie_aer.c
> > > @@ -738,6 +738,12 @@ void pcie_aer_root_init(PCIDevice *dev)
> > >                   PCI_ERR_ROOT_CMD_EN_MASK);
> > >      pci_set_long(dev->w1cmask + pos + PCI_ERR_ROOT_STATUS,
> > >                   PCI_ERR_ROOT_STATUS_REPORT_MASK);
> > > +    /* Bits 31:27 - Advanced Error Interrupt Message Number
> > 
> > This line is better moved to near definition of PCI_ERR_ROOT_IRQ.
> > Then here we can say 'PCI_ERR_ROOT_IRQ is RO but devices
> > change it using a device-specific method.'
> 
> ok.
> 
> > 
> > > +     * These bits are updated when the number of MSI messages changes.
> > > +     * By clearing the cmask, pcie devices can be migrated.
> > > +     */
> > > +    pci_set_long(dev->cmask + pos + PCI_ERR_ROOT_STATUS,
> > > +                 (1 << PCI_ERR_ROOT_IRQ_SHIFT) - 1);
> > 
> > ~PCI_ERR_ROOT_IRQ would be clearer I think.
> > 
> 
> agreed.
> 
> I will re-spin and post a v2.
> 
> Thanks,
> 
> -Jason