Re: [PATCH] tools/hvmloader: move shared_info to reserved memory area

[Keir Fraser <keir.xen@gmail.com>]

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On 24/10/2012 10:57, "Olaf Hering" <olaf@aepfle.de> wrote:

> # HG changeset patch
> # User Olaf Hering <olaf@aepfle.de>
> # Date 1351101387 -7200
> # Node ID 6a0c73ae9ce5cca72f788c0e0f8fd6872010d83e
> # Parent  22e08c9ac770db07c3c3e7c844aa7153050939f3
> tools/hvmloader: move shared_info to reserved memory area
> 
> Reserve a range of 1MB for the HVM shared info page at 0xFE700000. This
> area is already marked as reserved in the E820 map. The purpose of this
> change is to provide Linux PVonHVM guests with a fixed page outside of
> ordinary RAM. If the shared page is located in RAM it would be
> overwritten during a kexec boot.

I don't think hvmloader actually needs to map shared-info to the new
location, it justs needs to guarantee that this location is unused, and
document it so that it never *becomes* used in future.

Which can be as simple as the attached patch (in fact all the changes apart
from introducing GUEST_RESERVED_{START,END} are really cleaning up and
bug-fixing the out-of-space checks in the mem_hole_alloc/mem_alloc
functions).

This then just requires that the guest maps shared-info to FE700000 itself.
Should be quite easy. :)

 -- Keir

> Signed-off-by: Olaf Hering <olaf@aepfle.de>
> 
> diff -r 22e08c9ac770 -r 6a0c73ae9ce5 tools/firmware/hvmloader/config.h
> --- a/tools/firmware/hvmloader/config.h
> +++ b/tools/firmware/hvmloader/config.h
> @@ -68,6 +68,8 @@ extern unsigned long pci_mem_start, pci_
>  /* NB. ACPI_INFO_PHYSICAL_ADDRESS *MUST* match definition in acpi/dsdt.asl!
> */
>  #define ACPI_INFO_PHYSICAL_ADDRESS    0xFC000000
>  #define RESERVED_MEMORY_DYNAMIC       0xFC001000
> +#define HVM_SHARED_INFO_AREA          0xFE700000
> +#define HVM_SHARED_INFO_SIZE          0x00100000
>  
>  extern unsigned long scratch_start;
>  
> diff -r 22e08c9ac770 -r 6a0c73ae9ce5 tools/firmware/hvmloader/util.c
> --- a/tools/firmware/hvmloader/util.c
> +++ b/tools/firmware/hvmloader/util.c
> @@ -433,11 +433,18 @@ void *mem_alloc(uint32_t size, uint32_t
>      if ( align < 16 )
>          align = 16;
>  
> +retry:
>      s = (reserve + align) & ~(align - 1);
>      e = s + size - 1;
>  
>      BUG_ON((e < s) || (e >> PAGE_SHIFT) >= hvm_info->reserved_mem_pgstart);
>  
> +    /* Skip the shared info region */
> +    if (s <= HVM_SHARED_INFO_AREA && e >= HVM_SHARED_INFO_AREA) {
> +     reserve = HVM_SHARED_INFO_AREA + HVM_SHARED_INFO_SIZE - 1;
> +     goto retry;
> +    }
> +
>      while ( (reserve >> PAGE_SHIFT) != (e >> PAGE_SHIFT) )
>      {
>          reserve += PAGE_SIZE;
> @@ -765,7 +772,7 @@ struct shared_info *get_shared_info(void
>      xatp.domid = DOMID_SELF;
>      xatp.space = XENMAPSPACE_shared_info;
>      xatp.idx   = 0;
> -    xatp.gpfn  = mem_hole_alloc(1);
> +    xatp.gpfn  = HVM_SHARED_INFO_AREA >> PAGE_SHIFT;
>      shared_info = (struct shared_info *)(xatp.gpfn << PAGE_SHIFT);
>      if ( hypercall_memory_op(XENMEM_add_to_physmap, &xatp) != 0 )
>          BUG();
> 
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> http://lists.xen.org/xen-devel


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diff -r 22e08c9ac770 tools/firmware/hvmloader/config.h
--- a/tools/firmware/hvmloader/config.h	Wed Oct 24 17:51:48 2012 +0200
+++ b/tools/firmware/hvmloader/config.h	Wed Oct 24 04:01:24 2012 -0700
@@ -67,7 +67,15 @@ extern unsigned long pci_mem_start, pci_
 #define RESERVED_MEMBASE              0xFC000000
 /* NB. ACPI_INFO_PHYSICAL_ADDRESS *MUST* match definition in acpi/dsdt.asl! */
 #define ACPI_INFO_PHYSICAL_ADDRESS    0xFC000000
-#define RESERVED_MEMORY_DYNAMIC       0xFC001000
+#define RESERVED_MEMORY_DYNAMIC_START 0xFC001000
+#define RESERVED_MEMORY_DYNAMIC_END   0xFE000000
+/*
+ * GUEST_RESERVED: Physical address space reserved for guest use.
+ * This is not dynamically advertised to guests, so this range must *never*
+ * be used for any purpose by us, in future.
+ */
+#define GUEST_RESERVED_START          0xFE700000
+#define GUEST_RESERVED_END            0xFE800000
 
 extern unsigned long scratch_start;
 
diff -r 22e08c9ac770 tools/firmware/hvmloader/util.c
--- a/tools/firmware/hvmloader/util.c	Wed Oct 24 17:51:48 2012 +0200
+++ b/tools/firmware/hvmloader/util.c	Wed Oct 24 04:01:24 2012 -0700
@@ -416,13 +416,14 @@ void mem_hole_populate_ram(xen_pfn_t mfn
     }
 }
 
-static uint32_t reserve = RESERVED_MEMORY_DYNAMIC - 1;
+static uint32_t alloc_up = RESERVED_MEMORY_DYNAMIC_START - 1;
+static uint32_t alloc_down = RESERVED_MEMORY_DYNAMIC_END;
 
 xen_pfn_t mem_hole_alloc(uint32_t nr_mfns)
 {
-    hvm_info->reserved_mem_pgstart -= nr_mfns;
-    BUG_ON(hvm_info->reserved_mem_pgstart <= (reserve >> PAGE_SHIFT));
-    return hvm_info->reserved_mem_pgstart;
+    alloc_down -= nr_mfns << PAGE_SHIFT;
+    BUG_ON(alloc_up >= alloc_down);
+    return alloc_down >> PAGE_SHIFT;
 }
 
 void *mem_alloc(uint32_t size, uint32_t align)
@@ -433,18 +434,18 @@ void *mem_alloc(uint32_t size, uint32_t 
     if ( align < 16 )
         align = 16;
 
-    s = (reserve + align) & ~(align - 1);
+    s = (alloc_up + align) & ~(align - 1);
     e = s + size - 1;
 
-    BUG_ON((e < s) || (e >> PAGE_SHIFT) >= hvm_info->reserved_mem_pgstart);
+    BUG_ON((e < s) || (e >= alloc_down));
 
-    while ( (reserve >> PAGE_SHIFT) != (e >> PAGE_SHIFT) )
+    while ( (alloc_up >> PAGE_SHIFT) != (e >> PAGE_SHIFT) )
     {
-        reserve += PAGE_SIZE;
-        mem_hole_populate_ram(reserve >> PAGE_SHIFT, 1);
+        alloc_up += PAGE_SIZE;
+        mem_hole_populate_ram(alloc_up >> PAGE_SHIFT, 1);
     }
 
-    reserve = e;
+    alloc_up = e;
 
     return (void *)(unsigned long)s;
 }

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