From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001

From: Patrick Steinhardt <ps@pks.im>

Date: Thu, 21 Apr 2022 15:24:18 +1000

Subject: [PATCH] mm: Allow dynamically requesting additional memory regions

Currently, all platforms will set up their heap on initialization of the

platform code. While this works mostly fine, it poses some limitations

on memory management on us. Most notably, allocating big chunks of

memory in the gigabyte range would require us to pre-request this many

bytes from the firmware and add it to the heap from the beginning on

some platforms like EFI. As this isn't needed for most configurations,

it is inefficient and may even negatively impact some usecases when,

e.g., chainloading. Nonetheless, allocating big chunks of memory is

required sometimes, where one example is the upcoming support for the

Argon2 key derival function in LUKS2.

In order to avoid pre-allocating big chunks of memory, this commit

implements a runtime mechanism to add more pages to the system. When

a given allocation cannot be currently satisfied, we'll call a given

callback set up by the platform's own memory management subsystem,

asking it to add a memory area with at least "n" bytes. If this

succeeds, we retry searching for a valid memory region, which should

now succeed.

If this fails, we try asking for "n" bytes, possibly spread across

multiple regions, in hopes that region merging means that we end up

with enough memory for things to work out.

Signed-off-by: Patrick Steinhardt <ps@pks.im>

Signed-off-by: Daniel Axtens <dja@axtens.net>

Tested-by: Stefan Berger <stefanb@linux.ibm.com>

Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

Tested-by: Patrick Steinhardt <ps@pks.im>

(cherry picked from commit 887f98f0db43e33fba4ec1f85e42fae1185700bc)

---

 grub-core/kern/mm.c | 30 ++++++++++++++++++++++++++++++

 include/grub/mm.h   | 18 ++++++++++++++++++

 2 files changed, 48 insertions(+)

diff --git a/grub-core/kern/mm.c b/grub-core/kern/mm.c

index 1825dc8289..f2e27f263b 100644

--- a/grub-core/kern/mm.c

+++ b/grub-core/kern/mm.c

@@ -28,6 +28,9 @@

   - multiple regions may be used as free space. They may not be

   contiguous.

+  - if existing regions are insufficient to satisfy an allocation, a new

+  region can be requested from firmware.

+

   Regions are managed by a singly linked list, and the meta information is

   stored in the beginning of each region. Space after the meta information

   is used to allocate memory.

@@ -81,6 +84,7 @@

 grub_mm_region_t grub_mm_base;

+grub_mm_add_region_func_t grub_mm_add_region_fn;

 /* Get a header from the pointer PTR, and set *P and *R to a pointer

    to the header and a pointer to its region, respectively. PTR must

@@ -444,6 +448,32 @@ grub_memalign (grub_size_t align, grub_size_t size)

       count++;

       goto again;

+    case 1:

+      /* Request additional pages, contiguous */

+      count++;

+

+      if (grub_mm_add_region_fn != NULL &&

+          grub_mm_add_region_fn (size, GRUB_MM_ADD_REGION_CONSECUTIVE) == GRUB_ERR_NONE)

+	goto again;

+

+      /* fallthrough  */

+

+    case 2:

+      /* Request additional pages, anything at all */

+      count++;

+

+      if (grub_mm_add_region_fn != NULL)

+        {

+          /*

+           * Try again even if this fails, in case it was able to partially

+           * satisfy the request

+           */

+          grub_mm_add_region_fn (size, GRUB_MM_ADD_REGION_NONE);

+          goto again;

+        }

+

+      /* fallthrough */

+

     default:

       break;

     }

diff --git a/include/grub/mm.h b/include/grub/mm.h

index d81623d226..7c6f925ffd 100644

--- a/include/grub/mm.h

+++ b/include/grub/mm.h

@@ -20,6 +20,7 @@

 #ifndef GRUB_MM_H

 #define GRUB_MM_H	1

+#include <grub/err.h>

 #include <grub/types.h>

 #include <grub/symbol.h>

 #include <grub/err.h>

@@ -29,6 +30,23 @@

 # define NULL	((void *) 0)

 #endif

+#define GRUB_MM_ADD_REGION_NONE        0

+#define GRUB_MM_ADD_REGION_CONSECUTIVE (1 << 0)

+

+/*

+ * Function used to request memory regions of `grub_size_t` bytes. The second

+ * parameter is a bitfield of `GRUB_MM_ADD_REGION` flags.

+ */

+typedef grub_err_t (*grub_mm_add_region_func_t) (grub_size_t, unsigned int);

+

+/*

+ * Set this function pointer to enable adding memory-regions at runtime in case

+ * a memory allocation cannot be satisfied with existing regions.

+ */

+#ifndef GRUB_MACHINE_EMU

+extern grub_mm_add_region_func_t EXPORT_VAR(grub_mm_add_region_fn);

+#endif

+

 void grub_mm_init_region (void *addr, grub_size_t size);

 void *EXPORT_FUNC(grub_calloc) (grub_size_t nmemb, grub_size_t size);

 void *EXPORT_FUNC(grub_malloc) (grub_size_t size);