Re: [PATCH v10 49/59] i386/xen: handle HVMOP_get_param

[Paul Durrant]

On 01/02/2023 14:31, David Woodhouse wrote:
> From: Joao Martins <joao.m.martins@oracle.com>
>
> Which is used to fetch xenstore PFN and port to be used
> by the guest. This is preallocated by the toolstack when
> guest will just read those and use it straight away.
>
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
> ---
>   target/i386/kvm/xen-emu.c | 39 +++++++++++++++++++++++++++++++++++++++
>   1 file changed, 39 insertions(+)
>
> diff --git a/target/i386/kvm/xen-emu.c b/target/i386/kvm/xen-emu.c
> index 75e62bc02f..3d6ea7ca98 100644
> --- a/target/i386/kvm/xen-emu.c
> +++ b/target/i386/kvm/xen-emu.c
> @@ -762,6 +762,42 @@ out:
>       return true;
>   }
>   
> +static bool handle_get_param(struct kvm_xen_exit *exit, X86CPU *cpu,
> +                             uint64_t arg)
> +{
> +    CPUState *cs = CPU(cpu);
> +    struct xen_hvm_param hp;
> +    int err = 0;
> +
> +    /* No need for 32/64 compat handling */
> +    qemu_build_assert(sizeof(hp) == 16);
> +
> +    if (kvm_copy_from_gva(cs, arg, &hp, sizeof(hp))) {
> +        err = -EFAULT;
> +        goto out;
> +    }
> +
> +    if (hp.domid != DOMID_SELF && hp.domid != xen_domid) {
> +        err = -ESRCH;
> +        goto out;
> +    }
> +
> +    switch (hp.index) {
> +    case HVM_PARAM_STORE_PFN:
> +        hp.value = XEN_SPECIAL_PFN(XENSTORE);

Reviewed-by: Paul Durrant <paul@xen.org>

... but this reminds me... I don't think you have code to seed the grant 
table in any of the patches. It is guest ABI that the XenStore PFN is in 
entry 1 of the grant table.

> +        break;
> +    default:
> +        return false;
> +    }
> +
> +    if (kvm_copy_to_gva(cs, arg, &hp, sizeof(hp))) {
> +        err = -EFAULT;
> +    }
> +out:
> +    exit->u.hcall.result = err;
> +    return true;
> +}
> +
>   static int kvm_xen_hcall_evtchn_upcall_vector(struct kvm_xen_exit *exit,
>                                                 X86CPU *cpu, uint64_t arg)
>   {
> @@ -806,6 +842,9 @@ static bool kvm_xen_hcall_hvm_op(struct kvm_xen_exit *exit, 
> X86CPU *cpu,
>       case HVMOP_set_param:
>           return handle_set_param(exit, cpu, arg);
>   
> +    case HVMOP_get_param:
> +        return handle_get_param(exit, cpu, arg);
> +
>       default:
>           return false;
>       }