Re: [QEMU PATCH v8] xen/passthrough: use gsi to map pirq when dom0 is PVH

["Chen, Jiqian" <Jiqian.Chen@xxxxxxx>]

On 2024/10/22 04:55, Stewart Hildebrand wrote:
> On 10/16/24 02:28, Jiqian Chen wrote:
>> In PVH dom0, when passthrough a device to domU, QEMU code
>> xen_pt_realize->xc_physdev_map_pirq wants to use gsi, but in current codes
>> the gsi number is got from file /sys/bus/pci/devices/<sbdf>/irq, that is
>> wrong, because irq is not equal with gsi, they are in different spaces, so
>> pirq mapping fails.
>>
>> To solve above problem, use new interface of Xen, xc_pcidev_get_gsi to get
>> gsi and use xc_physdev_map_pirq_gsi to map pirq when dom0 is PVH.
>>
>> Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
>> Signed-off-by: Huang Rui <ray.huang@xxxxxxx>
>> Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
>> ---
>> Hi All,
>> This is v8 to support passthrough on Xen when dom0 is PVH.
>> v7->v8 change:
>> * Since xc_physdev_gsi_from_dev was renamed to xc_pcidev_get_gsi, changed it.
>> * Added xen_run_qemu_on_hvm to check if Qemu run on PV dom0, if not use 
>> xc_physdev_map_pirq_gsi to map pirq.
>> * Used CONFIG_XEN_CTRL_INTERFACE_VERSION to wrap the new part for 
>> compatibility.
>> * Added "#define DOMID_RUN_QEMU 0" to represent the id of domain that Qemu 
>> run on.
>>
>>
>> Best regards,
>> Jiqian Chen
>>
>>
>>
>> v6->v7 changes:
>> * Because the function of obtaining gsi was changed on the kernel and Xen 
>> side. Changed to use
>>   xc_physdev_gsi_from_dev, that requires passing in sbdf instead of irq.
>>
>> v5->v6 changes:
>> * Because the function of obtaining gsi was changed on the kernel and Xen 
>> side. Changed to use
>>   xc_physdev_gsi_from_irq, instead of gsi sysfs.
>> * Since function changed, removed the Review-by of Stefano.
>>
>> v4->v5 changes:
>> * Added Review-by Stefano.
>>
>> v3->v4 changes:
>> * Added gsi into struct XenHostPCIDevice and used gsi number that read from 
>> gsi sysfs
>>   if it exists, if there is no gsi sysfs, still use irq.
>>
>> v2->v3 changes:
>> * Due to changes in the implementation of the second patch on kernel 
>> side(that adds
>>   a new sysfs for gsi instead of a new syscall), so read gsi number from the 
>> sysfs of gsi.
>>
>> v1 and v2:
>> We can record the relation between gsi and irq, then when userspace(qemu) 
>> want
>> to use gsi, we can do a translation. The third patch of kernel(xen/privcmd: 
>> Add new syscall
>> to get gsi from irq) records all the relations in 
>> acpi_register_gsi_xen_pvh() when dom0
>> initialize pci devices, and provide a syscall for userspace to get the gsi 
>> from irq. The
>> third patch of xen(tools: Add new function to get gsi from irq) add a new 
>> function
>> xc_physdev_gsi_from_irq() to call the new syscall added on kernel side.
>> And then userspace can use that function to get gsi. Then 
>> xc_physdev_map_pirq() will success.
>>
>> Issues we encountered:
>> 1. failed to map pirq for gsi
>> Problem: qemu will call xc_physdev_map_pirq() to map a passthrough device's 
>> gsi to pirq in
>> function xen_pt_realize(). But failed.
>>
>> Reason: According to the implement of xc_physdev_map_pirq(), it needs gsi 
>> instead of irq,
>> but qemu pass irq to it and treat irq as gsi, it is got from file
>> /sys/bus/pci/devices/xxxx:xx:xx.x/irq in function xen_host_pci_device_get(). 
>> But actually
>> the gsi number is not equal with irq. They are in different space.
>> ---
>>  hw/xen/xen_pt.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
>>  hw/xen/xen_pt.h |  1 +
>>  2 files changed, 45 insertions(+)
>>
>> diff --git a/hw/xen/xen_pt.c b/hw/xen/xen_pt.c
>> index 3635d1b39f79..7f8139d20915 100644
>> --- a/hw/xen/xen_pt.c
>> +++ b/hw/xen/xen_pt.c
>> @@ -766,6 +766,41 @@ static void xen_pt_destroy(PCIDevice *d) {
>>  }
>>  /* init */
>>  
>> +#define PCI_SBDF(seg, bus, dev, func) \
>> +            ((((uint32_t)(seg)) << 16) | \
>> +            (PCI_BUILD_BDF(bus, PCI_DEVFN(dev, func))))
> 
> Nit: This macro looks generic and useful. Would it be better defined in
> include/hw/pci/pci.h?
> 
>> +
>> +#if CONFIG_XEN_CTRL_INTERFACE_VERSION >= 42000
>> +static bool xen_run_qemu_on_hvm(void)
> 
> This function name seems to imply "is qemu running on HVM?", but I think
> the question we're really trying to answer is whether the pcidev needs
> a GSI mapped. How about calling the function "xen_pt_needs_gsi" or
> similar?
> 
>> +{
>> +    xc_domaininfo_t info;
>> +
>> +    if (!xc_domain_getinfo_single(xen_xc, DOMID_RUN_QEMU, &info) &&
>> +        (info.flags & XEN_DOMINF_hvm_guest)) {
> 
> I think reading /sys/hypervisor/guest_type would allow you to get the
> same information without another hypercall.
> 
>> +        return true;
>> +    }
>> +
>> +    return false;
>> +}
>> +
>> +static int xen_map_pirq_for_gsi(PCIDevice *d, int *pirq)
> 
> Nit: s/xen_/xen_pt_/
> 
>> +{
>> +    int gsi;
>> +    XenPCIPassthroughState *s = XEN_PT_DEVICE(d);
>> +
>> +    gsi = xc_pcidev_get_gsi(xen_xc,
>> +                            PCI_SBDF(s->real_device.domain,
>> +                                     s->real_device.bus,
>> +                                     s->real_device.dev,
>> +                                     s->real_device.func));
>> +    if (gsi >= 0) {
>> +        return xc_physdev_map_pirq_gsi(xen_xc, xen_domid, gsi, pirq);
>> +    }
>> +
>> +    return gsi;
>> +}
>> +#endif
>> +
>>  static void xen_pt_realize(PCIDevice *d, Error **errp)
>>  {
>>      ERRP_GUARD();
>> @@ -847,7 +882,16 @@ static void xen_pt_realize(PCIDevice *d, Error **errp)
>>          goto out;
>>      }
>>  
>> +#if CONFIG_XEN_CTRL_INTERFACE_VERSION >= 42000
>> +    if (xen_run_qemu_on_hvm()) {
>> +        rc = xen_map_pirq_for_gsi(d, &pirq);
>> +    } else {
>> +        rc = xc_physdev_map_pirq(xen_xc, xen_domid, machine_irq, &pirq);
>> +    }
>> +#else
>>      rc = xc_physdev_map_pirq(xen_xc, xen_domid, machine_irq, &pirq);
>> +#endif
>> +
>>      if (rc < 0) {
>>          XEN_PT_ERR(d, "Mapping machine irq %u to pirq %i failed, (err: 
>> %d)\n",
>>                     machine_irq, pirq, errno);
>> diff --git a/hw/xen/xen_pt.h b/hw/xen/xen_pt.h
>> index 095a0f0365d4..a08b45b7fbae 100644
>> --- a/hw/xen/xen_pt.h
>> +++ b/hw/xen/xen_pt.h
>> @@ -36,6 +36,7 @@ void xen_pt_log(const PCIDevice *d, const char *f, ...) 
>> G_GNUC_PRINTF(2, 3);
>>  #  define XEN_PT_LOG_CONFIG(d, addr, val, len)
>>  #endif
>>  
>> +#define DOMID_RUN_QEMU 0
>>  
>>  /* Helper */
>>  #define XEN_PFN(x) ((x) >> XC_PAGE_SHIFT)
> 
What you said makes more sense. I will change this patch according to your 
comments. Thank you very much!

-- 
Best regards,
Jiqian Chen.