Re: [XEN PATCH v10 5/5] domctl: Add XEN_DOMCTL_gsi_permission to grant gsi

[Jan Beulich <jbeulich@xxxxxxxx>]

On 17.06.2024 11:00, Jiqian Chen wrote:
> Some type of domain don't have PIRQs, like PVH, it doesn't do
> PHYSDEVOP_map_pirq for each gsi. When passthrough a device
> to guest base on PVH dom0, callstack
> pci_add_dm_done->XEN_DOMCTL_irq_permission will fail at function
> domain_pirq_to_irq, because PVH has no mapping of gsi, pirq and
> irq on Xen side.
> What's more, current hypercall XEN_DOMCTL_irq_permission requires
> passing in pirq, it is not suitable for dom0 that doesn't have
> PIRQs.
> 
> So, add a new hypercall XEN_DOMCTL_gsi_permission to grant the
> permission of irq(translate from gsi) to dumU when dom0 has no
> PIRQs.
> 
> Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
> Signed-off-by: Huang Rui <ray.huang@xxxxxxx>
> Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
> ---
> RFC: it needs review and needs to wait for the corresponding third patch on 
> linux kernel side to be merged.
> ---
>  tools/include/xenctrl.h            |  5 +++
>  tools/libs/ctrl/xc_domain.c        | 15 +++++++
>  tools/libs/light/libxl_pci.c       | 67 +++++++++++++++++++++++++++---
>  xen/arch/x86/domctl.c              | 43 +++++++++++++++++++
>  xen/arch/x86/include/asm/io_apic.h |  2 +
>  xen/arch/x86/io_apic.c             | 17 ++++++++
>  xen/arch/x86/mpparse.c             |  3 +-
>  xen/include/public/domctl.h        |  8 ++++
>  xen/xsm/flask/hooks.c              |  1 +
>  9 files changed, 153 insertions(+), 8 deletions(-)
> 
> diff --git a/tools/include/xenctrl.h b/tools/include/xenctrl.h
> index a0381f74d24b..f3feb6848e25 100644
> --- a/tools/include/xenctrl.h
> +++ b/tools/include/xenctrl.h
> @@ -1382,6 +1382,11 @@ int xc_domain_irq_permission(xc_interface *xch,
>                               uint32_t pirq,
>                               bool allow_access);
>  
> +int xc_domain_gsi_permission(xc_interface *xch,
> +                             uint32_t domid,
> +                             uint32_t gsi,
> +                             bool allow_access);
> +
>  int xc_domain_iomem_permission(xc_interface *xch,
>                                 uint32_t domid,
>                                 unsigned long first_mfn,
> diff --git a/tools/libs/ctrl/xc_domain.c b/tools/libs/ctrl/xc_domain.c
> index f2d9d14b4d9f..8540e84fda93 100644
> --- a/tools/libs/ctrl/xc_domain.c
> +++ b/tools/libs/ctrl/xc_domain.c
> @@ -1394,6 +1394,21 @@ int xc_domain_irq_permission(xc_interface *xch,
>      return do_domctl(xch, &domctl);
>  }
>  
> +int xc_domain_gsi_permission(xc_interface *xch,
> +                             uint32_t domid,
> +                             uint32_t gsi,
> +                             bool allow_access)
> +{
> +    struct xen_domctl domctl = {
> +        .cmd = XEN_DOMCTL_gsi_permission,
> +        .domain = domid,
> +        .u.gsi_permission.gsi = gsi,
> +        .u.gsi_permission.allow_access = allow_access,
> +    };
> +
> +    return do_domctl(xch, &domctl);
> +}
> +
>  int xc_domain_iomem_permission(xc_interface *xch,
>                                 uint32_t domid,
>                                 unsigned long first_mfn,
> diff --git a/tools/libs/light/libxl_pci.c b/tools/libs/light/libxl_pci.c
> index 376f91759ac6..f027f22c0028 100644
> --- a/tools/libs/light/libxl_pci.c
> +++ b/tools/libs/light/libxl_pci.c
> @@ -1431,6 +1431,9 @@ static void pci_add_dm_done(libxl__egc *egc,
>      uint32_t flag = XEN_DOMCTL_DEV_RDM_RELAXED;
>      uint32_t domainid = domid;
>      bool isstubdom = libxl_is_stubdom(ctx, domid, &domainid);
> +#ifdef CONFIG_X86
> +    xc_domaininfo_t info;
> +#endif
>  
>      /* Convenience aliases */
>      bool starting = pas->starting;
> @@ -1516,14 +1519,39 @@ static void pci_add_dm_done(libxl__egc *egc,
>              rc = ERROR_FAIL;
>              goto out;
>          }
> -        r = xc_domain_irq_permission(ctx->xch, domid, irq, 1);
> +#ifdef CONFIG_X86
> +        /* If dom0 doesn't have PIRQs, need to use xc_domain_gsi_permission 
> */
> +        r = xc_domain_getinfo_single(ctx->xch, 0, &info);

Hard-coded 0 is imposing limitations. Ideally you would use DOMID_SELF, but
I didn't check if that can be used with the underlying hypercall(s). Otherwise
you want to pass the actual domid of the local domain here.

>          if (r < 0) {
> -            LOGED(ERROR, domainid,
> -                  "xc_domain_irq_permission irq=%d (error=%d)", irq, r);
> +            LOGED(ERROR, domainid, "getdomaininfo failed (error=%d)", errno);
>              fclose(f);
>              rc = ERROR_FAIL;
>              goto out;
>          }
> +        if (info.flags & XEN_DOMINF_hvm_guest &&

You want to parenthesize the & here.

> +            !(info.arch_config.emulation_flags & XEN_X86_EMU_USE_PIRQ) &&
> +            gsi > 0) {

So if gsi < 0 failure of xc_domain_getinfo_single() would needlessly result
in failure of this function?

> --- a/xen/arch/x86/domctl.c
> +++ b/xen/arch/x86/domctl.c
> @@ -36,6 +36,7 @@
>  #include <asm/xstate.h>
>  #include <asm/psr.h>
>  #include <asm/cpu-policy.h>
> +#include <asm/io_apic.h>
>  
>  static int update_domain_cpu_policy(struct domain *d,
>                                      xen_domctl_cpu_policy_t *xdpc)
> @@ -237,6 +238,48 @@ long arch_do_domctl(
>          break;
>      }
>  
> +    case XEN_DOMCTL_gsi_permission:
> +    {
> +        unsigned int gsi = domctl->u.gsi_permission.gsi;
> +        int irq;
> +        bool allow = domctl->u.gsi_permission.allow_access;

See my earlier comments on this conversion of 8 bits into just one.

> +        /* Check all pads are zero */
> +        ret = -EINVAL;
> +        for ( i = 0;
> +              i < sizeof(domctl->u.gsi_permission.pad) /
> +                  sizeof(domctl->u.gsi_permission.pad[0]);

Please don't open-code ARRAY_SIZE().

> +              ++i )
> +            if ( domctl->u.gsi_permission.pad[i] )
> +                goto out;
> +
> +        /*
> +         * If current domain is PV or it has PIRQ flag, it has a mapping
> +         * of gsi, pirq and irq, so it should use XEN_DOMCTL_irq_permission
> +         * to grant irq permission.
> +         */
> +        ret = -EOPNOTSUPP;
> +        if ( is_pv_domain(currd) || has_pirq(currd) )
> +            goto out;

I'm curious what other x86 maintainers think: I for one would not impose such
an artificial restriction.

> +        ret = -EINVAL;
> +        if ( gsi >= nr_irqs_gsi || (irq = gsi_2_irq(gsi)) < 0 )
> +            goto out;
> +
> +        ret = -EPERM;
> +        if ( !irq_access_permitted(currd, irq) ||
> +             xsm_irq_permission(XSM_HOOK, d, irq, allow) )
> +            goto out;
> +
> +        if ( allow )
> +            ret = irq_permit_access(d, irq);
> +        else
> +            ret = irq_deny_access(d, irq);
> +
> +    out:

Please use a less generic name for such a label local to just one case
block. However, with ..

> +        break;

.. this being all that's done here: Why have a label in the first place?

Jan