Re: [Qemu-devel] [RFC Patch] xen/pt: Emulate FLR capability

[Jan Beulich]

On 29.08.2019 11:02, Chao Gao wrote:
> Currently, for a HVM on Xen, no reset method is virtualized. So in a VM's
> perspective, assigned devices cannot be reset. But some devices rely on PCI
> reset to recover from hardware hangs. When being assigned to a VM, those
> devices cannot be reset and won't work any longer if a hardware hang occurs.
> We have to reboot VM to trigger PCI reset on host to recover the device.

Did you consider a hot-unplug, reset (by host), hot-plug cycle instead?

> +static int xen_pt_devctl_reg_write(XenPCIPassthroughState *s,
> +                                   XenPTReg *cfg_entry, uint16_t *val,
> +                                   uint16_t dev_value, uint16_t valid_mask)
> +{
> +    if (s->real_device.is_resetable && (*val & PCI_EXP_DEVCTL_BCR_FLR)) {
> +        xen_pt_reset(s);
> +    }
> +    return xen_pt_word_reg_write(s, cfg_entry, val, dev_value, valid_mask);

I think you also need to clear the bit before handing on the request,
such that reads will always observe it clear.

Jan