PXELINUX: Add bios memscan function

We can mark the memory region occupied by the PXE stack as SMT_TERMINAL
provided that KeepPXE isn't set. Historically some very old
non-relocatable kernel images (memtest86+) have a load address that
falls within the PXE stack region, so we need to attempt to load into
that region if at all possible.

Signed-off-by: Matt Fleming <matt.fleming@intel.com>

1 files changed, 35 insertions, 0 deletions

diff --git a/core/fs/pxe/bios.c b/core/fs/pxe/bios.c
index 81aa715c..5f618248 100644
--- a/core/fs/pxe/bios.c
+++ b/core/fs/pxe/bios.c
@@ -1,4 +1,5 @@
 #include <syslinux/firmware.h>
+#include <syslinux/memscan.h>
 #include <core.h>
 #include "pxe.h"
 #include <net.h>
@@ -10,6 +11,9 @@ static uint16_t real_base_mem;	   /* Amount of DOS memory after freeing */
 static bool has_gpxe;
 static uint32_t gpxe_funcs;
 
+static addr_t pxe_code_start, pxe_code_size;
+static addr_t pxe_data_start, pxe_data_size;
+
 /*
  * Validity check on possible !PXE structure in buf
  * return 1 for success, 0 for failure.
@@ -88,6 +92,29 @@ static const struct pxenv_t *memory_scan_for_pxenv_struct(void)
     return memory_scan(0x10000, is_pxenv);
 }
 
+static int pxelinux_scan_memory(scan_memory_callback_t callback, void *data)
+{
+    int rv = 0;
+
+    /*
+     * If we are planning on calling unload_pxe() and unmapping the PXE
+     * region before we transfer control away from PXELINUX we can mark
+     * that region as SMT_TERMINAL to indicate that the region will
+     * become free at some point in the future.
+     */
+    if (!KeepPXE) {
+	dprintf("Marking PXE code region 0x%x - 0x%x as SMT_TERMINAL\n",
+		pxe_code_start, pxe_code_start + pxe_code_size);
+	rv = callback(data, pxe_code_start, pxe_code_size, SMT_TERMINAL);
+
+	dprintf("Marking PXE data region 0x%x - 0x%x as SMT_TERMINAL\n",
+		pxe_data_start, pxe_data_start + pxe_data_size);
+	rv = callback(data, pxe_data_start, pxe_data_size, SMT_TERMINAL);
+    }
+
+    return rv;
+}
+
 /*
  * Find the !PXE structure; we search for the following, in order:
  *
@@ -204,6 +231,14 @@ int pxe_init(bool quiet)
 	printf("UNDI data segment at %04X len %04X\n", data_seg, data_len);
     }
 
+    pxe_code_start = code_seg << 4;
+    pxe_code_size = code_len;
+
+    pxe_data_start = data_seg << 4;
+    pxe_data_size = data_len;
+
+    syslinux_memscan_new(pxelinux_scan_memory);
+
     code_seg = code_seg + ((code_len + 15) >> 4);
     data_seg = data_seg + ((data_len + 15) >> 4);