Re: [Xen-devel] [PATCH v2 12/18] xen: setup Xen specific data for PVH

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Tue, Oct 09, 2018 at 01:03:11PM +0200, Juergen Gross wrote:
> Initialize the needed Xen specific data. This is:
> 
> - the Xen start of day page containing the console and Xenstore ring
>   page PFN and event channel
> - the grant table
> - the shared info page
> 
> Set the RSDP address for the guest from the start_info page passed
> as boot parameter.
> 
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
>  grub-core/kern/i386/xen/pvh.c | 107 
> ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 107 insertions(+)
> 
> diff --git a/grub-core/kern/i386/xen/pvh.c b/grub-core/kern/i386/xen/pvh.c
> index b4933b454..93ed68245 100644
> --- a/grub-core/kern/i386/xen/pvh.c
> +++ b/grub-core/kern/i386/xen/pvh.c
> @@ -24,6 +24,7 @@
>  #include <grub/xen.h>
>  #include <grub/i386/linux.h>
>  #include <grub/machine/kernel.h>
> +#include <xen/hvm/params.h>
>  #include <xen/memory.h>
>  
>  struct xen_machine_mmap_entry
> @@ -39,6 +40,7 @@ static struct { char _entry[32]; } hypercall_page[128]
>    __attribute__ ((aligned (GRUB_XEN_PAGE_SIZE)));
>  
>  static grub_uint32_t xen_cpuid_base;
> +static struct start_info grub_xen_start_page;
>  static struct xen_machine_mmap_entry map[128];
>  static unsigned int nr_map_entries;
>  
> @@ -104,6 +106,36 @@ grub_xen_hypercall (grub_uint32_t callno, grub_uint32_t 
> a0,
>    return __res;
>  }
>  
> +static grub_uint32_t
> +grub_xen_get_param (int idx)
> +{
> +  struct xen_hvm_param xhv;
> +  int r;
> +
> +  xhv.domid = DOMID_SELF;
> +  xhv.index = idx;
> +  r = grub_xen_hypercall (__HYPERVISOR_hvm_op, HVMOP_get_param,
> +                       (grub_uint32_t) (&xhv), 0, 0, 0, 0);
> +  if (r < 0)
> +    grub_xen_early_halt ();
> +  return xhv.value;
> +}
> +
> +static void *
> +grub_xen_add_physmap (unsigned int space, void *addr)
> +{
> +  struct xen_add_to_physmap xatp;
> +
> +  xatp.domid = DOMID_SELF;
> +  xatp.idx = 0;
> +  xatp.space = space;
> +  xatp.gpfn = (grub_addr_t) addr >> GRUB_XEN_LOG_PAGE_SIZE;
> +  if (grub_xen_hypercall (__HYPERVISOR_memory_op, XENMEM_add_to_physmap,
> +                       (grub_uint32_t) (&xatp), 0, 0, 0, 0))
> +    grub_xen_early_halt ();
> +  return addr;
> +}
> +
>  static void
>  grub_xen_sort_mmap (void)
>  {
> @@ -190,12 +222,87 @@ grub_xen_get_mmap (void)
>    grub_xen_sort_mmap ();
>  }
>  
> +static grub_uint64_t
> +grub_xen_find_page (grub_uint64_t start)
> +{
> +  unsigned int i, j;
> +  grub_uint64_t last = start;
> +
> +  /* Try to find a e820 map hole below 4G. */

Doing this is kind of dangerous, what if you end up placing something
on top of an MMIO region (either emulated or from a real passthrough
device)?

> +  for (i = 0; i < nr_map_entries; i++)
> +    {
> +      if (last > map[i].addr + map[i].len)
> +     continue;
> +      if (last < map[i].addr)
> +     return last;
> +      if ((map[i].addr >> 32) || ((map[i].addr + map[i].len) >> 32))
> +     break;
> +      last = map[i].addr + map[i].len;
> +    }
> +    if (i == nr_map_entries)
> +      return last;
> +
> +  /* No hole found, use the highest RAM page below 4G and reserve it. */

I would rather use a RAM page and populate if afterwards, so that the
memory map returned by the Xen hypercall still matches the current
physmap, or else update the memmap using XENMEM_set_memory_map?

This has the nasty side effect of shattering the p2m though.

Thanks, Roger.

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