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

[Juergen Gross]

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?

> 
>> +  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.

Right, and this would be a noticeable performance hit.


Juergen