efi/x86: Limit EFI old memory map to SGI UV machines

We carry a quirk in the x86 EFI code to switch back to an older
method of mapping the EFI runtime services memory regions, because
it was deemed risky at the time to implement a new method without
providing a fallback to the old method in case problems arose.

Such problems did arise, but they appear to be limited to SGI UV1
machines, and so these are the only ones for which the fallback gets
enabled automatically (via a DMI quirk). The fallback can be enabled
manually as well, by passing efi=old_map, but there is very little
evidence that suggests that this is something that is being relied
upon in the field.

Given that UV1 support is not enabled by default by the distros
(Ubuntu, Fedora), there is no point in carrying this fallback code
all the time if there are no other users. So let's move it into the
UV support code, and document that efi=old_map now requires this
support code to be enabled.

Note that efi=old_map has been used in the past on other SGI UV
machines to work around kernel regressions in production, so we
keep the option to enable it by hand, but only if the kernel was
built with UV support.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200113172245.27925-8-ardb@kernel.org

1 files changed, 14 insertions, 7 deletions

diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
index eb421cb35108..fe46ddf6c761 100644
--- a/arch/x86/platform/efi/quirks.c
+++ b/arch/x86/platform/efi/quirks.c
@@ -384,10 +384,10 @@ static void __init efi_unmap_pages(efi_memory_desc_t *md)
 
 	/*
 	 * To Do: Remove this check after adding functionality to unmap EFI boot
-	 * services code/data regions from direct mapping area because
-	 * "efi=old_map" maps EFI regions in swapper_pg_dir.
+	 * services code/data regions from direct mapping area because the UV1
+	 * memory map maps EFI regions in swapper_pg_dir.
 	 */
-	if (efi_enabled(EFI_OLD_MEMMAP))
+	if (efi_have_uv1_memmap())
 		return;
 
 	/*
@@ -558,7 +558,7 @@ out:
 	return ret;
 }
 
-static const struct dmi_system_id sgi_uv1_dmi[] = {
+static const struct dmi_system_id sgi_uv1_dmi[] __initconst = {
 	{ NULL, "SGI UV1",
 		{	DMI_MATCH(DMI_PRODUCT_NAME,	"Stoutland Platform"),
 			DMI_MATCH(DMI_PRODUCT_VERSION,	"1.0"),
@@ -581,8 +581,15 @@ void __init efi_apply_memmap_quirks(void)
 	}
 
 	/* UV2+ BIOS has a fix for this issue.  UV1 still needs the quirk. */
-	if (dmi_check_system(sgi_uv1_dmi))
-		set_bit(EFI_OLD_MEMMAP, &efi.flags);
+	if (dmi_check_system(sgi_uv1_dmi)) {
+		if (IS_ENABLED(CONFIG_X86_UV)) {
+			set_bit(EFI_UV1_MEMMAP, &efi.flags);
+		} else {
+			pr_warn("EFI runtime disabled, needs CONFIG_X86_UV=y on UV1\n");
+			clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);
+			efi_memmap_unmap();
+		}
+	}
 }
 
 /*
@@ -720,7 +727,7 @@ void efi_recover_from_page_fault(unsigned long phys_addr)
 	/*
 	 * Make sure that an efi runtime service caused the page fault.
 	 * "efi_mm" cannot be used to check if the page fault had occurred
-	 * in the firmware context because efi=old_map doesn't use efi_pgd.
+	 * in the firmware context because the UV1 memmap doesn't use efi_pgd.
 	 */
 	if (efi_rts_work.efi_rts_id == EFI_NONE)
 		return;