grub2/0200-ieee1275-claim-more-memory.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Daniel Axtens <dja@axtens.net>
Date: Wed, 15 Apr 2020 23:28:29 +1000
Subject: [PATCH] ieee1275: claim more memory

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>
---
 grub-core/kern/ieee1275/init.c | 81 +++++++++++++++++++++++++++++++++---------
 docs/grub-dev.texi             |  6 ++--
 2 files changed, 69 insertions(+), 18 deletions(-)

diff --git a/grub-core/kern/ieee1275/init.c b/grub-core/kern/ieee1275/init.c
index 0dcd114ce54..c61d91a0285 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 _end[];
@@ -147,16 +148,45 @@ 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)
@@ -170,10 +200,6 @@ 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
@@ -185,6 +211,18 @@ 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;
@@ -193,10 +231,12 @@ 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;
@@ -205,13 +245,22 @@ 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
 
diff --git a/docs/grub-dev.texi b/docs/grub-dev.texi
index a55af53fd45..008bd7a3c34 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