Re: [Xen-devel] [PATCH v5 07/12] x86/hyperv: setup hypercall page

["Durrant, Paul" <pdurrant@xxxxxxxxxxxx>]

> -----Original Message-----
> From: Wei Liu <wei.liu.xen@xxxxxxxxx> On Behalf Of Wei Liu
> Sent: 29 January 2020 20:20
> To: Xen Development List <xen-devel@xxxxxxxxxxxxxxxxxxxx>
> Cc: Durrant, Paul <pdurrant@xxxxxxxxxxxx>; Michael Kelley
> <mikelley@xxxxxxxxxxxxx>; Wei Liu <liuwe@xxxxxxxxxxxxx>; Jan Beulich
> <jbeulich@xxxxxxxx>; Andrew Cooper <andrew.cooper3@xxxxxxxxxx>; Wei Liu
> <wl@xxxxxxx>; Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Subject: [PATCH v5 07/12] x86/hyperv: setup hypercall page
> 
> Hyper-V uses a technique called overlay page for its hypercall page. It
> will insert a backing page to the guest when the hypercall functionality
> is enabled. That means we can use a page that is not backed by real
> memory for hypercall page.
> 
> Use the top-most addressable page for that purpose. Adjust e820 code
> accordingly.
> 
> We also need to register Xen's guest OS ID to Hyper-V. Use 0x3 as the
> vendor ID. Fix the comment in hyperv-tlfs.h while at it.
> 
> Signed-off-by: Wei Liu <liuwe@xxxxxxxxxxxxx>
> ---
> v5:
> 1. use hypervisor_reserve_top_pages
> 2. add a macro for hypercall page mfn
> 3. address other misc comments
> 
> v4:
> 1. Use fixmap
> 2. Follow routines listed in TLFS
> ---
>  xen/arch/x86/e820.c                     |  5 +++
>  xen/arch/x86/guest/hyperv/hyperv.c      | 57 +++++++++++++++++++++++--
>  xen/include/asm-x86/guest/hyperv-tlfs.h |  5 ++-
>  xen/include/asm-x86/guest/hyperv.h      |  3 ++
>  4 files changed, 65 insertions(+), 5 deletions(-)
> 
> diff --git a/xen/arch/x86/e820.c b/xen/arch/x86/e820.c
> index 3892c9cfb7..99643f3ea0 100644
> --- a/xen/arch/x86/e820.c
> +++ b/xen/arch/x86/e820.c
> @@ -343,6 +343,7 @@ static unsigned long __init find_max_pfn(void)
>  {
>      unsigned int i;
>      unsigned long max_pfn = 0;
> +    unsigned long top_pfn = ((1ull << paddr_bits) - 1) >> PAGE_SHIFT;
> 
>      for (i = 0; i < e820.nr_map; i++) {
>          unsigned long start, end;
> @@ -357,6 +358,10 @@ static unsigned long __init find_max_pfn(void)
>              max_pfn = end;
>      }
> 
> +    top_pfn -= hypervisor_reserve_top_pages();
> +    if ( max_pfn >= top_pfn )
> +        max_pfn = top_pfn;
> +
>      return max_pfn;
>  }
> 
> diff --git a/xen/arch/x86/guest/hyperv/hyperv.c
> b/xen/arch/x86/guest/hyperv/hyperv.c
> index 8d38313d7a..2bedcc438c 100644
> --- a/xen/arch/x86/guest/hyperv/hyperv.c
> +++ b/xen/arch/x86/guest/hyperv/hyperv.c
> @@ -19,15 +19,26 @@
>   * Copyright (c) 2019 Microsoft.
>   */
>  #include <xen/init.h>
> +#include <xen/version.h>
> 
> +#include <asm/fixmap.h>
>  #include <asm/guest.h>
>  #include <asm/guest/hyperv-tlfs.h>
> +#include <asm/processor.h>
> 
>  struct ms_hyperv_info __read_mostly ms_hyperv;
> 
> -static const struct hypervisor_ops ops = {
> -    .name = "Hyper-V",
> -};
> +static uint64_t generate_guest_id(void)
> +{
> +    uint64_t id;
> +
> +    id = (uint64_t)HV_XEN_VENDOR_ID << 48;
> +    id |= (xen_major_version() << 16) | xen_minor_version();
> +
> +    return id;

I think this should use the hv_guest_os_id union. You can then set the values 
using the bit-fields and return the raw.

  Paul

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