[PATCH v2 0/3] ieee1275: find and claim more memory

[PATCH v2 0/3] ieee1275: find and claim more memory

[Daniel Axtens]

I've posted a couple of RFC patches that attempted to claim some more
memory on ieee1275 platforms, which is necessary for the verifiers to
do their work. The RFCs were a bit unsatisfactory and also it turns
out they broke in some corner cases.

This, I believe, is a proper, upstream-worthy solution for getting
more memory on ieee1275 platforms and powerpc-ieee1275 in
particular. It is also, sadly, an set of quite complex solutions, as
the commit messages for patches 2 and 3 show! It seems this is the
cost of broad platform support and backwards compatibility.

There's no reason for this to go into 2.06.

Kind regards,
Daniel

v2: fix the bug where I mixed up model and compatible.

Daniel Axtens (3):
  ieee1275: drop HEAP_MAX_ADDR, HEAP_MIN_SIZE
  ieee1275: claim more memory
  ieee1275: request memory with ibm,client-architecture-support

 docs/grub-dev.texi               |   6 +-
 grub-core/kern/ieee1275/cmain.c  |   3 +
 grub-core/kern/ieee1275/init.c   | 238 ++++++++++++++++++++++++++-----
 include/grub/ieee1275/ieee1275.h |   6 +
 4 files changed, 218 insertions(+), 35 deletions(-)

-- 
2.27.0

[PATCH v2 1/3] ieee1275: drop HEAP_MAX_ADDR, HEAP_MIN_SIZE

[Daniel Axtens]

HEAP_MAX_ADDR is confusing. Currently it is set to 32MB, except
on ieee1275 on x86, where it is 64MB.

There is a comment which purports to explain it:

/* If possible, we will avoid claiming heap above this address, because it
   seems to cause relocation problems with OSes that link at 4 MiB */

This doesn't make a lot of sense when the constants are well above 4MB
already. It was not always this way. Prior to
commit 7b5d0fe4440c ("Increase heap limit") in 2010, HEAP_MAX_SIZE and
HEAP_MAX_ADDR were indeed 4MB. However, when the constants were increased
the comment was left unchanged.

It's been over a decade. It doesn't seem like we have problems with
claims over 4MB on powerpc or x86 ieee1275. (sparc does things completely
differently and never used the constant.)

Drop the constant and the check.

The only use of HEAP_MIN_SIZE was to potentially override the
HEAP_MAX_ADDR check. It is now unused. Remove it.

Signed-off-by: Daniel Axtens <dja@axtens.net>
---
 grub-core/kern/ieee1275/init.c | 17 -----------------
 1 file changed, 17 deletions(-)

diff --git a/grub-core/kern/ieee1275/init.c b/grub-core/kern/ieee1275/init.c
index 7a1ebdf94e06..c81cfc0320ae 100644
--- a/grub-core/kern/ieee1275/init.c
+++ b/grub-core/kern/ieee1275/init.c
@@ -46,9 +46,6 @@
 #endif
 #include <grub/lockdown.h>
 
-/* The minimal heap size we can live with. */
-#define HEAP_MIN_SIZE		(unsigned long) (2 * 1024 * 1024)
-
 /* The maximum heap size we're going to claim */
 #ifdef __i386__
 #define HEAP_MAX_SIZE		(unsigned long) (64 * 1024 * 1024)
@@ -56,14 +53,6 @@
 #define HEAP_MAX_SIZE		(unsigned long) (32 * 1024 * 1024)
 #endif
 
-/* If possible, we will avoid claiming heap above this address, because it
-   seems to cause relocation problems with OSes that link at 4 MiB */
-#ifdef __i386__
-#define HEAP_MAX_ADDR		(unsigned long) (64 * 1024 * 1024)
-#else
-#define HEAP_MAX_ADDR		(unsigned long) (32 * 1024 * 1024)
-#endif
-
 extern char _start[];
 extern char _end[];
 
@@ -184,12 +173,6 @@ heap_init (grub_uint64_t addr, grub_uint64_t len, grub_memory_type_t type,
   if (*total + len > HEAP_MAX_SIZE)
     len = HEAP_MAX_SIZE - *total;
 
-  /* Avoid claiming anything above HEAP_MAX_ADDR, if possible. */
-  if ((addr < HEAP_MAX_ADDR) &&				/* if it's too late, don't bother */
-      (addr + len > HEAP_MAX_ADDR) &&				/* if it wasn't available anyway, don't bother */
-      (*total + (HEAP_MAX_ADDR - addr) > HEAP_MIN_SIZE))	/* only limit ourselves when we can afford to */
-     len = HEAP_MAX_ADDR - addr;
-
   /* In theory, firmware should already prevent this from happening by not
      listing our own image in /memory/available.  The check below is intended
      as a safeguard in case that doesn't happen.  However, it doesn't protect
-- 
2.27.0

[PATCH v2 2/3] ieee1275: claim more memory

[Daniel Axtens]

On powerpc-ieee1275, we are running out of memory trying to verify
anything. This is because:

 - we have to load an entire file into memory to verify it. This is
   extremely difficult to change with appended signatures.
 - We only have 32MB of heap.
 - Distro kernels are now often around 30MB.

So we want to claim more memory from OpenFirmware for our heap.

There are some complications:

 - The grub mm code isn't the only thing that will make claims on
   memory from OpenFirmware:

    * PFW/SLOF will have claimed some for their own use.

    * The ieee1275 loader will try to find other bits of memory that we
      haven't claimed to place the kernel and initrd when we go to boot.

    * Once we load Linux, it will also try to claim memory. It claims
      memory without any reference to /memory/available, it just starts
      at min(top of RMO, 768MB) and works down. So we need to avoid this
      area. See arch/powerpc/kernel/prom_init.c as of v5.11.

 - The smallest amount of memory a ppc64 KVM guest can have is 256MB.
   It doesn't work with distro kernels but can work with custom kernels.
   We should maintain support for that. (ppc32 can boot with even less,
   and we shouldn't break that either.)

 - Even if a VM has more memory, the memory OpenFirmware makes available
   as Real Memory Area can be restricted. A freshly created LPAR on a
   PowerVM machine is likely to have only 256MB available to OpenFirmware
   even if it has many gigabytes of memory allocated.

EFI systems will attempt to allocate 1/4th of the available memory,
clamped to between 1M and 1600M. That seems like a good sort of
approach, we just need to figure out if 1/4 is the right fraction
for us.

We don't know in advance how big the kernel and initrd are going to be,
which makes figuring out how much memory we can take a bit tricky.

To figure out how much memory we should leave unused, I looked at:

 - an Ubuntu 20.04.1 ppc64le pseries KVM guest:
    vmlinux: ~30MB
    initrd:  ~50MB

 - a RHEL8.2 ppc64le pseries KVM guest:
    vmlinux: ~30MB
    initrd:  ~30MB

Ubuntu VMs struggle to boot with just 256MB under SLOF.
RHEL likewise has a higher minimum supported memory figure.
So lets first consider a distro kernel and 512MB of addressible memory.
(This is the default case for anything booting under PFW.) Say we lose
131MB to PFW (based on some tests). This leaves us 381MB. 1/4 of 381MB
is ~95MB. That should be enough to verify a 30MB vmlinux and should
leave plenty of space to load Linux and the initrd.

If we consider 256MB of RMA under PFW, we have just 125MB remaining. 1/4
of that is a smidge under 32MB, which gives us very poor odds of verifying
a distro-sized kernel. However, if we need 80MB just to put the kernel
and initrd in memory, we can't claim any more than 45MB anyway. So 1/4
will do. We'll come back to this later.

grub is always built as a 32-bit binary, even if it's loading a ppc64
kernel. So we can't address memory beyond 4GB. This gives a natural cap
of 1GB for powerpc-ieee1275.

Also apply this 1/4 approach to i386-ieee1275, but keep the 32MB cap.

make check still works for both i386 and powerpc and I've booted
powerpc grub with this change under SLOF and PFW.

Signed-off-by: Daniel Axtens <dja@axtens.net>
---
 docs/grub-dev.texi             |  6 ++-
 grub-core/kern/ieee1275/init.c | 81 +++++++++++++++++++++++++++-------
 2 files changed, 69 insertions(+), 18 deletions(-)

diff --git a/docs/grub-dev.texi b/docs/grub-dev.texi
index a834b3a9c32c..5dc7c285cf87 100644
--- a/docs/grub-dev.texi
+++ b/docs/grub-dev.texi
@@ -1047,7 +1047,9 @@ space is limited to 4GiB. GRUB allocates pages from EFI for its heap, at most
 1.6 GiB.
 
 On i386-ieee1275 and powerpc-ieee1275 GRUB uses same stack as IEEE1275.
-It allocates at most 32MiB for its heap.
+
+On i386-ieee1275, GRUB allocates at most 32MiB for its heap. On
+powerpc-ieee1275, GRUB allocates up to 1GiB.
 
 On sparc64-ieee1275 stack is 256KiB and heap is 2MiB.
 
@@ -1075,7 +1077,7 @@ In short:
 @item i386-qemu               @tab 60 KiB  @tab < 4 GiB
 @item *-efi                   @tab ?       @tab < 1.6 GiB
 @item i386-ieee1275           @tab ?       @tab < 32 MiB
-@item powerpc-ieee1275        @tab ?       @tab < 32 MiB
+@item powerpc-ieee1275        @tab ?       @tab < 1 GiB
 @item sparc64-ieee1275        @tab 256KiB  @tab 2 MiB
 @item arm-uboot               @tab 256KiB  @tab 2 MiB
 @item mips(el)-qemu_mips      @tab 2MiB    @tab 253 MiB
diff --git a/grub-core/kern/ieee1275/init.c b/grub-core/kern/ieee1275/init.c
index c81cfc0320ae..3053a59fe9e1 100644
--- a/grub-core/kern/ieee1275/init.c
+++ b/grub-core/kern/ieee1275/init.c
@@ -46,11 +46,12 @@
 #endif
 #include <grub/lockdown.h>
 
-/* The maximum heap size we're going to claim */
+/* The maximum heap size we're going to claim. Not used by sparc.
+   We allocate 1/4 of the available memory under 4G, up to this limit. */
 #ifdef __i386__
 #define HEAP_MAX_SIZE		(unsigned long) (64 * 1024 * 1024)
-#else
-#define HEAP_MAX_SIZE		(unsigned long) (32 * 1024 * 1024)
+#else // __powerpc__
+#define HEAP_MAX_SIZE		(unsigned long) (1 * 1024 * 1024 * 1024)
 #endif
 
 extern char _start[];
@@ -146,16 +147,45 @@ grub_claim_heap (void)
 				 + GRUB_KERNEL_MACHINE_STACK_SIZE), 0x200000);
 }
 #else
-/* Helper for grub_claim_heap.  */
+/* Helper for grub_claim_heap on powerpc. */
+static int
+heap_size (grub_uint64_t addr, grub_uint64_t len, grub_memory_type_t type,
+	   void *data)
+{
+  grub_uint32_t total = *(grub_uint32_t *)data;
+
+  if (type != GRUB_MEMORY_AVAILABLE)
+    return 0;
+
+  /* Do not consider memory beyond 4GB */
+  if (addr > 0xffffffffUL)
+    return 0;
+
+  if (addr + len > 0xffffffffUL)
+    len = 0xffffffffUL - addr;
+
+  total += len;
+  *(grub_uint32_t *)data = total;
+
+  return 0;
+}
+
 static int
 heap_init (grub_uint64_t addr, grub_uint64_t len, grub_memory_type_t type,
 	   void *data)
 {
-  unsigned long *total = data;
+  grub_uint32_t total = *(grub_uint32_t *)data;
 
   if (type != GRUB_MEMORY_AVAILABLE)
     return 0;
 
+  /* Do not consider memory beyond 4GB */
+  if (addr > 0xffffffffUL)
+    return 0;
+
+  if (addr + len > 0xffffffffUL)
+    len = 0xffffffffUL - addr;
+
   if (grub_ieee1275_test_flag (GRUB_IEEE1275_FLAG_NO_PRE1_5M_CLAIM))
     {
       if (addr + len <= 0x180000)
@@ -169,10 +199,6 @@ heap_init (grub_uint64_t addr, grub_uint64_t len, grub_memory_type_t type,
     }
   len -= 1; /* Required for some firmware.  */
 
-  /* Never exceed HEAP_MAX_SIZE  */
-  if (*total + len > HEAP_MAX_SIZE)
-    len = HEAP_MAX_SIZE - *total;
-
   /* In theory, firmware should already prevent this from happening by not
      listing our own image in /memory/available.  The check below is intended
      as a safeguard in case that doesn't happen.  However, it doesn't protect
@@ -184,6 +210,18 @@ heap_init (grub_uint64_t addr, grub_uint64_t len, grub_memory_type_t type,
       len = 0;
     }
 
+  /* If this block contains 0x30000000 (768MB), do not claim below that.
+     Linux likes to claim memory at min(RMO top, 768MB) and works down
+     without reference to /memory/available. */
+  if ((addr < 0x30000000) && ((addr + len) > 0x30000000))
+    {
+      len = len - (0x30000000 - addr);
+      addr = 0x30000000;
+    }
+
+  if (len > total)
+    len = total;
+
   if (len)
     {
       grub_err_t err;
@@ -192,10 +230,12 @@ heap_init (grub_uint64_t addr, grub_uint64_t len, grub_memory_type_t type,
       if (err)
 	return err;
       grub_mm_init_region ((void *) (grub_addr_t) addr, len);
+      total -= len;
     }
 
-  *total += len;
-  if (*total >= HEAP_MAX_SIZE)
+  *(grub_uint32_t *)data = total;
+
+  if (total == 0)
     return 1;
 
   return 0;
@@ -204,13 +244,22 @@ heap_init (grub_uint64_t addr, grub_uint64_t len, grub_memory_type_t type,
 static void 
 grub_claim_heap (void)
 {
-  unsigned long total = 0;
+  grub_uint32_t total = 0;
 
   if (grub_ieee1275_test_flag (GRUB_IEEE1275_FLAG_FORCE_CLAIM))
-    heap_init (GRUB_IEEE1275_STATIC_HEAP_START, GRUB_IEEE1275_STATIC_HEAP_LEN,
-	       1, &total);
-  else
-    grub_machine_mmap_iterate (heap_init, &total);
+    {
+      heap_init (GRUB_IEEE1275_STATIC_HEAP_START, GRUB_IEEE1275_STATIC_HEAP_LEN,
+		 1, &total);
+      return;
+    }
+
+  grub_machine_mmap_iterate (heap_size, &total);
+
+  total = total / 4;
+  if (total > HEAP_MAX_SIZE)
+    total = HEAP_MAX_SIZE;
+
+  grub_machine_mmap_iterate (heap_init, &total);
 }
 #endif
 
-- 
2.27.0

[PATCH v2 3/3] ieee1275: request memory with ibm, client-architecture-support

[Daniel Axtens]

On PowerVM, the first time we boot a Linux partition, we may only get
256MB of real memory area, even if the partition has more memory.

This isn't really enough. Fortunately, the Power Architecture Platform
Reference (PAPR) defines a method we can call to ask for more memory.
This is part of the broad and powerful ibm,client-architecture-support
(CAS) method.

CAS can do an enormous amount of things on a PAPR platform: as well as
asking for memory, you can set the supported processor level, the interrupt
controller, hash vs radix mmu, and so on. We want to touch as little of
this as possible because we don't want to step on the toes of the future OS.

If:

 - we are running under what we think is PowerVM (compatible property of /
   begins with "IBM"), and

 - the full amount of RMA is less than 512MB (as determined by the reg
   property of /memory)

then call CAS as follows: (refer to the Linux on Power Architecture
Reference, LoPAR, which is public, at B.5.2.3):

 - Use the "any" PVR value and supply 2 option vectors.

 - Set option vector 1 (PowerPC Server Processor Architecture Level)
   to "ignore".

 - Set option vector 2 with default or Linux-like options, including a
   min-rma-size of 512MB.

This will cause a CAS reboot and the partition will restart with 512MB
of RMA. Grub will notice the 512MB and not call CAS again.

(A partition can be configured with only 256MB of memory, which would
mean this request couldn't be satisfied, but PFW refuses to load with
only 256MB of memory, so it's a bit moot. SLOF will run fine with 256MB,
but we will never call CAS under qemu/SLOF because /compatible won't
begin with "IBM".)

One of the first things Linux does while still running under OpenFirmware
is to call CAS with a much fuller set of options (including asking for
512MB of memory). This includes a much more restrictive set of PVR values
and processor support levels, and this will induce another reboot. On this
reboot grub will again notice the higher RMA, and not call CAS. We will get
to Linux, Linux will call CAS but because the values are now set for Linux
this will not induce another CAS reboot and we will finally boot.

On all subsequent boots, everything will be configured with 512MB of RMA
and all the settings Linux likes, so there will be no further CAS reboots.

(phyp is super sticky with the RMA size - it persists even on cold boots.
So if you've ever booted Linux in a partition, you'll probably never have
grub call CAS. It'll only ever fire the first time a partition loads grub,
or if you deliberately lower the amount of memory your partition has below
512MB.)

Signed-off-by: Daniel Axtens <dja@axtens.net>
---
 grub-core/kern/ieee1275/cmain.c  |   3 +
 grub-core/kern/ieee1275/init.c   | 144 ++++++++++++++++++++++++++++++-
 include/grub/ieee1275/ieee1275.h |   6 ++
 3 files changed, 151 insertions(+), 2 deletions(-)

diff --git a/grub-core/kern/ieee1275/cmain.c b/grub-core/kern/ieee1275/cmain.c
index 20cbbd761ec3..cc98811f4f99 100644
--- a/grub-core/kern/ieee1275/cmain.c
+++ b/grub-core/kern/ieee1275/cmain.c
@@ -124,6 +124,9 @@ grub_ieee1275_find_options (void)
 	      break;
 	    }
 	}
+
+      if (grub_strncmp (tmp, "IBM,", 4) == 0)
+	grub_ieee1275_set_flag (GRUB_IEEE1275_FLAG_CAN_TRY_CAS_FOR_MORE_MEMORY);
     }
 
   if (is_smartfirmware)
diff --git a/grub-core/kern/ieee1275/init.c b/grub-core/kern/ieee1275/init.c
index 3053a59fe9e1..5faf4e736074 100644
--- a/grub-core/kern/ieee1275/init.c
+++ b/grub-core/kern/ieee1275/init.c
@@ -241,6 +241,135 @@ heap_init (grub_uint64_t addr, grub_uint64_t len, grub_memory_type_t type,
   return 0;
 }
 
+/* How much memory does OF believe it has? (regardless of whether
+   it's accessible or not) */
+static grub_err_t
+grub_ieee1275_total_mem (grub_uint64_t *total)
+{
+  grub_ieee1275_phandle_t root;
+  grub_ieee1275_phandle_t memory;
+  grub_uint32_t reg[4];
+  grub_ssize_t reg_size;
+  grub_uint32_t address_cells = 1;
+  grub_uint32_t size_cells = 1;
+  grub_uint64_t size;
+
+  /* If we fail to get to the end, report 0. */
+  *total = 0;
+
+  /* Determine the format of each entry in `reg'.  */
+  grub_ieee1275_finddevice ("/", &root);
+  grub_ieee1275_get_integer_property (root, "#address-cells", &address_cells,
+				      sizeof address_cells, 0);
+  grub_ieee1275_get_integer_property (root, "#size-cells", &size_cells,
+				      sizeof size_cells, 0);
+
+  if (size_cells > address_cells)
+    address_cells = size_cells;
+
+  /* Load `/memory/reg'.  */
+  if (grub_ieee1275_finddevice ("/memory", &memory))
+    return grub_error (GRUB_ERR_UNKNOWN_DEVICE,
+		       "couldn't find /memory node");
+  if (grub_ieee1275_get_integer_property (memory, "reg", reg,
+					  sizeof reg, &reg_size))
+    return grub_error (GRUB_ERR_UNKNOWN_DEVICE,
+		       "couldn't examine /memory/reg property");
+  if (reg_size < 0 || (grub_size_t) reg_size > sizeof (reg))
+    return grub_error (GRUB_ERR_UNKNOWN_DEVICE,
+                       "/memory response buffer exceeded");
+
+  if (grub_ieee1275_test_flag (GRUB_IEEE1275_FLAG_BROKEN_ADDRESS_CELLS))
+    {
+      address_cells = 1;
+      size_cells = 1;
+    }
+
+  /* Decode only the size */
+  size = reg[address_cells];
+  if (size_cells == 2)
+    size = (size << 32) | reg[address_cells + 1];
+
+  *total = size;
+
+  return grub_errno;
+}
+
+/* Based on linux - arch/powerpc/kernel/prom_init.c */
+struct option_vector2 {
+	grub_uint8_t byte1;
+	grub_uint16_t reserved;
+	grub_uint32_t real_base;
+	grub_uint32_t real_size;
+	grub_uint32_t virt_base;
+	grub_uint32_t virt_size;
+	grub_uint32_t load_base;
+	grub_uint32_t min_rma;
+	grub_uint32_t min_load;
+	grub_uint8_t min_rma_percent;
+	grub_uint8_t max_pft_size;
+} __attribute__((packed));
+
+struct pvr_entry {
+	  grub_uint32_t mask;
+	  grub_uint32_t entry;
+};
+
+struct cas_vector {
+    struct {
+      struct pvr_entry terminal;
+    } pvr_list;
+    grub_uint8_t num_vecs;
+    grub_uint8_t vec1_size;
+    grub_uint8_t vec1;
+    grub_uint8_t vec2_size;
+    struct option_vector2 vec2;
+} __attribute__((packed));
+
+/* Call ibm,client-architecture-support to try to get more RMA.
+   We ask for 512MB which should be enough to verify a distro kernel.
+   We ignore most errors: if we don't succeed we'll proceed with whatever
+   memory we have. */
+static void
+grub_ieee1275_ibm_cas (void)
+{
+  int rc;
+  grub_ieee1275_ihandle_t root;
+  struct cas_args {
+    struct grub_ieee1275_common_hdr common;
+    grub_ieee1275_cell_t method;
+    grub_ieee1275_ihandle_t ihandle;
+    grub_ieee1275_cell_t cas_addr;
+    grub_ieee1275_cell_t result;
+  } args;
+  struct cas_vector vector = {
+    .pvr_list = { { 0x00000000, 0xffffffff } }, /* any processor */
+    .num_vecs = 2 - 1,
+    .vec1_size = 0,
+    .vec1 = 0x80, /* ignore */
+    .vec2_size = 1 + sizeof(struct option_vector2) - 2,
+    .vec2 = {
+      0, 0, -1, -1, -1, -1, -1, 512, -1, 0, 48
+    },
+  };
+
+  INIT_IEEE1275_COMMON (&args.common, "call-method", 3, 2);
+  args.method = (grub_ieee1275_cell_t)"ibm,client-architecture-support";
+  rc = grub_ieee1275_open("/", &root);
+  if (rc) {
+	  grub_error (GRUB_ERR_IO, "could not open root when trying to call CAS");
+	  return;
+  }
+  args.ihandle = root;
+  args.cas_addr = (grub_ieee1275_cell_t)&vector;
+
+  grub_printf("Calling ibm,client-architecture-support...");
+  IEEE1275_CALL_ENTRY_FN (&args);
+  grub_printf("done\n");
+
+  grub_ieee1275_close(root);
+}
+
 static void 
 grub_claim_heap (void)
 {
@@ -248,11 +377,22 @@ grub_claim_heap (void)
 
   if (grub_ieee1275_test_flag (GRUB_IEEE1275_FLAG_FORCE_CLAIM))
     {
-      heap_init (GRUB_IEEE1275_STATIC_HEAP_START, GRUB_IEEE1275_STATIC_HEAP_LEN,
-		 1, &total);
+      heap_init (GRUB_IEEE1275_STATIC_HEAP_START,
+		 GRUB_IEEE1275_STATIC_HEAP_LEN, 1, &total);
       return;
     }
 
+  if (grub_ieee1275_test_flag (GRUB_IEEE1275_FLAG_CAN_TRY_CAS_FOR_MORE_MEMORY))
+    {
+      grub_uint64_t rma_size;
+      grub_err_t err;
+
+      err = grub_ieee1275_total_mem (&rma_size);
+      /* if we have an error, don't call CAS, just hope for the best */
+      if (!err && rma_size < (512 * 1024 * 1024))
+	grub_ieee1275_ibm_cas();
+    }
+
   grub_machine_mmap_iterate (heap_size, &total);
 
   total = total / 4;
diff --git a/include/grub/ieee1275/ieee1275.h b/include/grub/ieee1275/ieee1275.h
index 73e2f4644751..18c479b668ce 100644
--- a/include/grub/ieee1275/ieee1275.h
+++ b/include/grub/ieee1275/ieee1275.h
@@ -148,6 +148,12 @@ enum grub_ieee1275_flag
   GRUB_IEEE1275_FLAG_CURSORONOFF_ANSI_BROKEN,
 
   GRUB_IEEE1275_FLAG_RAW_DEVNAMES,
+
+  /* On PFW, the first time we boot a Linux partition, we may only get 256MB
+     of real memory area, even if the partition has more memory. Set this flag
+     if we think we're running under PFW. Then, if this flag is set, and the
+     RMA is only 256MB in size, try asking for more with CAS. */
+  GRUB_IEEE1275_FLAG_CAN_TRY_CAS_FOR_MORE_MEMORY,
 };
 
 extern int EXPORT_FUNC(grub_ieee1275_test_flag) (enum grub_ieee1275_flag flag);
-- 
2.27.0