Re: [RFC PATCH v2 08/26] ARM: GICv3 ITS: map device and LPIs to the ITS on physdev_op hypercall

[Stefano Stabellini <sstabellini@kernel.org>]

On Thu, 22 Dec 2016, Andre Przywara wrote:
> To get MSIs from devices forwarded to a CPU, we need to name the device
> and its MSIs by mapping them to an ITS.
> Since this involves queueing commands to the ITS command queue, we can't
> really afford to do this during the guest's runtime, as this would open
> up a denial-of-service attack vector.
> So we require every device with MSI interrupts to be mapped explicitly by
> Dom0. For Dom0 itself we can just use the existing PCI physdev_op
> hypercalls, which the existing Linux kernel issues already.
> So upon receipt of this hypercall we map the device to the hardware ITS
> and prepare it to be later mapped by the virtual ITS by using the very
> same device ID (for Dom0 only).
> Also we ask for mapping 32 LPIs to cover 32 MSIs that the device may
> use.
> 
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> ---
>  xen/arch/arm/physdev.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/xen/arch/arm/physdev.c b/xen/arch/arm/physdev.c
> index 27bbbda..d9e6be3 100644
> --- a/xen/arch/arm/physdev.c
> +++ b/xen/arch/arm/physdev.c
> @@ -9,11 +9,35 @@
>  #include <xen/lib.h>
>  #include <xen/errno.h>
>  #include <xen/sched.h>
> +#include <xen/guest_access.h>
> +#include <asm/gic-its.h>
>  #include <asm/hypercall.h>
>  
>  
>  int do_physdev_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
>  {
> +    struct physdev_manage_pci manage;
> +    struct domain *dom0;
> +    u32 devid;
> +    int ret;
> +
> +    switch (cmd)
> +    {
> +        case PHYSDEVOP_manage_pci_add:
> +        case PHYSDEVOP_manage_pci_remove:
> +            if ( copy_from_guest(&manage, arg, 1) != 0 )
> +                return -EFAULT;
> +
> +            dom0 = hardware_domain;

Please don't effectively name dom0 hardware_domain, just use
hardware_domain directly.


> +            devid = manage.bus << 8 | manage.devfn;
> +            /* Allocate an ITS device table with space for 32 MSIs */
> +            ret = gicv3_its_map_device(dom0, devid, devid, 5,
> +                                       cmd == PHYSDEVOP_manage_pci_add);

Why 32? Is it an arbitrary number? Shouldn't we figure out exactly the
number of events the device need?


> +            put_domain(dom0);

Where is the correspondent get_domain?


> +            return ret;
> +    }
> +
>      gdprintk(XENLOG_DEBUG, "PHYSDEVOP cmd=%d: not implemented\n", cmd);
>      return -ENOSYS;
>  }
> -- 
> 2.9.0
> 

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