Re: [RFC XEN PATCH v3 3/3] libxl: Use gsi instead of irq for mapping pirq

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Dec 11, 2023 at 12:40:09AM +0800, Jiqian Chen wrote:
> In PVH dom0, it uses the linux local interrupt mechanism,
> when it allocs irq for a gsi, it is dynamic, and follow
> the principle of applying first, distributing first. And
> the irq number is alloced from small to large, but the
> applying gsi number is not, may gsi 38 comes before gsi
> 28, that causes the irq number is not equal with the gsi
> number. And when passthrough a device, xl wants to use
> gsi to map pirq, see pci_add_dm_done->xc_physdev_map_pirq,
> but the gsi number is got from file
> /sys/bus/pci/devices/<sbdf>/irq in current code, so it
> will fail when mapping.
> 
> So, use real gsi number read from gsi sysfs.
> 
> Co-developed-by: Huang Rui <ray.huang@xxxxxxx>
> Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
> ---
>  tools/libs/light/libxl_pci.c | 18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/tools/libs/light/libxl_pci.c b/tools/libs/light/libxl_pci.c
> index 96cb4da079..9e75f0c263 100644
> --- a/tools/libs/light/libxl_pci.c
> +++ b/tools/libs/light/libxl_pci.c
> @@ -1416,7 +1416,7 @@ static void pci_add_dm_done(libxl__egc *egc,
>      char *sysfs_path;
>      FILE *f;
>      unsigned long long start, end, flags, size;
> -    int irq, i;
> +    int gsi, i;
>      int r;
>      uint32_t flag = XEN_DOMCTL_DEV_RDM_RELAXED;
>      uint32_t domainid = domid;
> @@ -1439,7 +1439,7 @@ static void pci_add_dm_done(libxl__egc *egc,
>                             pci->bus, pci->dev, pci->func);
>      f = fopen(sysfs_path, "r");
>      start = end = flags = size = 0;
> -    irq = 0;
> +    gsi = 0;

unsigned int (so it matches the fscanf format), and initialized at
definition.

>  
>      if (f == NULL) {
>          LOGED(ERROR, domainid, "Couldn't open %s", sysfs_path);
> @@ -1478,26 +1478,26 @@ static void pci_add_dm_done(libxl__egc *egc,
>      fclose(f);
>      if (!pci_supp_legacy_irq())
>          goto out_no_irq;
> -    sysfs_path = GCSPRINTF(SYSFS_PCI_DEV"/"PCI_BDF"/irq", pci->domain,
> +    sysfs_path = GCSPRINTF(SYSFS_PCI_DEV"/"PCI_BDF"/gsi", pci->domain,
>                                  pci->bus, pci->dev, pci->func);

You need to keep the fallback mechanism of reading the irq node, or
else xl would stop working on any kernel that doesn't expose this
sysfs node, you would break passthrough on all current Linux versions.

Thanks, Roger.