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

[Roger Pau Monné]

On Fri, Oct 19, 2018 at 06:39:50PM +0200, Juergen Gross wrote:
> On 19/10/2018 18:10, Roger Pau Monné wrote:
> > 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 <address@hidden>
> >> ---
> >>  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)?
> 
> Shouldn't those be marked as "Reserved" in the memory map?

I don't think BARs are guaranteed to be in areas marked as reserved in
the memory map. Unless you also scan for PCI devices and make sure
there's no device with a BAR in the area you are attempting to
populate I think the above is not safe.

Thanks, Roger.