x86/setup: Move trim_snb_memory() later in setup_arch() to fix boot hangs

Commit

  a799c2bd29d1 ("x86/setup: Consolidate early memory reservations")

moved reservation of the memory inaccessible by Sandy Bride integrated
graphics very early, and, as a result, on systems with such devices
the first 1M was reserved by trim_snb_memory() which prevented the
allocation of the real mode trampoline and made the boot hang very
early.

Since the purpose of trim_snb_memory() is to prevent problematic pages
ever reaching the graphics device, it is safe to reserve these pages
after memblock allocations are possible.

Move trim_snb_memory() later in boot so that it will be called after
reserve_real_mode() and make comments describing trim_snb_memory()
operation more elaborate.

 [ bp: Massage a bit. ]

Fixes: a799c2bd29d1 ("x86/setup: Consolidate early memory reservations")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Hugh Dickins <hughd@google.com>
Link: https://lkml.kernel.org/r/f67d3e03-af90-f790-baf4-8d412fe055af@infradead.org

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 776fc9b..e93283e 100644 (file)
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -633,11 +633,16 @@ static void __init trim_snb_memory(void)
        printk(KERN_DEBUG "reserving inaccessible SNB gfx pages\n");
 
        /*
-        * Reserve all memory below the 1 MB mark that has not
-        * already been reserved.
+        * SandyBridge integrated graphics devices have a bug that prevents
+        * them from accessing certain memory ranges, namely anything below
+        * 1M and in the pages listed in bad_pages[] above.
+        *
+        * To avoid these pages being ever accessed by SNB gfx devices
+        * reserve all memory below the 1 MB mark and bad_pages that have
+        * not already been reserved at boot time.
         */
        memblock_reserve(0, 1<<20);
-       
+
        for (i = 0; i < ARRAY_SIZE(bad_pages); i++) {
                if (memblock_reserve(bad_pages[i], PAGE_SIZE))
                        printk(KERN_WARNING "failed to reserve 0x%08lx\n",
@@ -746,8 +751,6 @@ static void __init early_reserve_memory(void)
 
        reserve_ibft_region();
        reserve_bios_regions();
-
-       trim_snb_memory();
 }
 
 /*
@@ -1081,6 +1084,13 @@ void __init setup_arch(char **cmdline_p)
 
        reserve_real_mode();
 
+       /*
+        * Reserving memory causing GPU hangs on Sandy Bridge integrated
+        * graphics devices should be done after we allocated memory under
+        * 1M for the real mode trampoline.
+        */
+       trim_snb_memory();
+
        init_mem_mapping();
 
        idt_setup_early_pf();