Re: [Xen-devel] [PATCH 4/8] x86/hyperv: setup hypercall page

[Michael Kelley <mikelley@xxxxxxxxxxxxx>]

From: Wei Liu <wei.liu.xen@xxxxxxxxx> On Behalf Of Wei Liu  Sent: Sunday, 
December 29, 2019 10:34 AM
> 
> Signed-off-by: Wei Liu <liuwe@xxxxxxxxxxxxx>
> ---
>  xen/arch/x86/guest/hyperv/hyperv.c | 41 +++++++++++++++++++++++++++---
>  1 file changed, 38 insertions(+), 3 deletions(-)
> 
> diff --git a/xen/arch/x86/guest/hyperv/hyperv.c 
> b/xen/arch/x86/guest/hyperv/hyperv.c
> index c6a26c5453..438910c8cb 100644
> --- a/xen/arch/x86/guest/hyperv/hyperv.c
> +++ b/xen/arch/x86/guest/hyperv/hyperv.c
> @@ -19,16 +19,17 @@
>   * Copyright (c) 2019 Microsoft.
>   */
>  #include <xen/init.h>
> +#include <xen/domain_page.h>
> 
>  #include <asm/guest.h>
>  #include <asm/guest/hyperv-tlfs.h>
> 
>  struct ms_hyperv_info __read_mostly ms_hyperv;
> 
> -static const struct hypervisor_ops ops = {
> -    .name = "Hyper-V",
> -};
> +void *hv_hypercall;
> +static struct page_info *hv_hypercall_page;
> 
> +static const struct hypervisor_ops ops;
>  const struct hypervisor_ops *__init hyperv_probe(void)
>  {
>      uint32_t eax, ebx, ecx, edx;
> @@ -71,6 +72,40 @@ const struct hypervisor_ops *__init hyperv_probe(void)
>      return &ops;
>  }
> 
> +static void __init setup_hypercall_page(void)
> +{
> +    union hv_x64_msr_hypercall_contents hypercall_msr;
> +
> +    /* Unfortunately there isn't a really good way to unwind Xen to
> +     * not use Hyper-V hooks, so panic if anything goes wrong.
> +     *
> +     * In practice if page allocation fails this early on it is
> +     * unlikely we can get a working system later.
> +     */
> +    hv_hypercall_page = alloc_domheap_page(NULL, 0);
> +    if ( !hv_hypercall_page )
> +        panic("Failed to allocate Hyper-V hypercall page\n");
> +
> +    hv_hypercall = __map_domain_page_global(hv_hypercall_page);
> +    if ( !hv_hypercall )
> +        panic("Failed to map Hyper-V hypercall page\n");
> +
> +    rdmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
> +    hypercall_msr.enable = 1;
> +    hypercall_msr.guest_physical_address = page_to_maddr(hv_hypercall_page);

The "guest_physical_address" field is actually the guest physical page number.
So the physical address needs to be right shifted 12 bits before being stored
here.  I'd recommend using HV_HYP_PAGE_SHIFT from hyperv-tlfs.h as
the shift value; it was introduced to deal with the possibility that the page
size used and expected by the Hyper-V interface is different from the page
size used by the guest VM (which can happen on ARM64, though not on x86).

Michael

> +    wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
> +}
> +
> +static void __init setup(void)
> +{
> +    setup_hypercall_page();
> +}
> +
> +static const struct hypervisor_ops ops = {
> +    .name = "Hyper-V",
> +    .setup = setup,
> +};
> +
>  /*
>   * Local variables:
>   * mode: C
> --
> 2.20.1


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