[PATCH v2] x86/platform/UV: Fix support for EFI_OLD_MEMMAP after BIOS callback updates

[Alex Thorlton <athorlton@sgi.com>]

Some time ago, we brought our UV BIOS callback code up to speed with the
new EFI memory mapping scheme, in commit:

    d1be84a232e3 ("x86/uv: Update uv_bios_call() to use efi_call_virt_pointer()")

By leveraging some changes that I made to a few of the EFI runtime
callback mechanisms, in commit:

    80e75596079f ("efi: Convert efi_call_virt() to efi_call_virt_pointer()")

This got everything running smoothly on UV, with the new EFI mapping
code.  However, this left one, small loose end, in that EFI_OLD_MEMMAP
(a.k.a. efi=old_map) will no longer work on UV, on kernels that include
the aforementioned changes.

At the time this was not a major issue (in fact, it still really isn't),
but there's no reason that EFI_OLD_MEMMAP *shouldn't* work on our
systems.  This commit adds a check into uv_bios_call, to see if we have
the EFI_OLD_MEMMAP bit set in efi.flags.  If it is set, we fall back to
using our old callback method, which uses efi_call directly on the __va
of our function pointer.

v2: Invert if-statement and add unlikely() hint.

Signed-off-by: Alex Thorlton <athorlton@sgi.com>
Cc: Mike Travis <travis@sgi.com>
Cc: Russ Anderson <rja@sgi.com>
Cc: Dimitri Sivanich <sivanich@sgi.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: x86@kernel.org
---
 arch/x86/platform/uv/bios_uv.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/x86/platform/uv/bios_uv.c b/arch/x86/platform/uv/bios_uv.c
index b4d5e95..d1f7422 100644
--- a/arch/x86/platform/uv/bios_uv.c
+++ b/arch/x86/platform/uv/bios_uv.c
@@ -40,7 +40,15 @@ s64 uv_bios_call(enum uv_bios_cmd which, u64 a1, u64 a2, u64 a3, u64 a4, u64 a5)
 		 */
 		return BIOS_STATUS_UNIMPLEMENTED;
 
-	ret = efi_call_virt_pointer(tab, function, (u64)which, a1, a2, a3, a4, a5);
+	/*
+	 * If EFI_OLD_MEMMAP is set, we need to fall back to using our old EFI
+	 * callback method, which uses efi_call directly, with the kernel page tables.
+	 */
+	if (unlikely(test_bit(EFI_OLD_MEMMAP, &efi.flags)))
+		ret = efi_call((void *)__va(tab->function), (u64)which, a1, a2, a3, a4, a5);
+	else
+		ret = efi_call_virt_pointer(tab, function, (u64)which, a1, a2, a3, a4, a5);
+
 	return ret;
 }
 EXPORT_SYMBOL_GPL(uv_bios_call);
-- 
1.8.5.6