arm64: efi: Force the use of SetVirtualAddressMap() on Altra machines

Ampere Altra machines are reported to misbehave when the SetTime() EFI
runtime service is called after ExitBootServices() but before calling
SetVirtualAddressMap(). Given that the latter is horrid, pointless and
explicitly documented as optional by the EFI spec, we no longer invoke
it at boot if the configured size of the VA space guarantees that the
EFI runtime memory regions can remain mapped 1:1 like they are at boot
time.

On Ampere Altra machines, this results in SetTime() calls issued by the
rtc-efi driver triggering synchronous exceptions during boot.  We can
now recover from those without bringing down the system entirely, due to
commit 23715a26c8d81291 ("arm64: efi: Recover from synchronous
exceptions occurring in firmware"). However, it would be better to avoid
the issue entirely, given that the firmware appears to remain in a funny
state after this.

So attempt to identify these machines based on the 'family' field in the
type #1 SMBIOS record, and call SetVirtualAddressMap() unconditionally
in that case.

Tested-by: Alexandru Elisei <[email protected]>
Signed-off-by: Ard Biesheuvel <[email protected]>

1 files changed, 16 insertions, 1 deletions

diff --git a/drivers/firmware/efi/libstub/arm64-stub.c b/drivers/firmware/efi/libstub/arm64-stub.c
index 259e4b852d63..f9de5217ea65 100644
--- a/drivers/firmware/efi/libstub/arm64-stub.c
+++ b/drivers/firmware/efi/libstub/arm64-stub.c
@@ -15,6 +15,21 @@
 
 #include "efistub.h"
 
+static bool system_needs_vamap(void)
+{
+	const u8 *type1_family = efi_get_smbios_string(1, family);
+
+	/*
+	 * Ampere Altra machines crash in SetTime() if SetVirtualAddressMap()
+	 * has not been called prior.
+	 */
+	if (!type1_family || strcmp(type1_family, "Altra"))
+		return false;
+
+	efi_warn("Working around broken SetVirtualAddressMap()\n");
+	return true;
+}
+
 efi_status_t check_platform_features(void)
 {
 	u64 tg;
@@ -24,7 +39,7 @@ efi_status_t check_platform_features(void)
 	 * UEFI runtime regions 1:1 and so calling SetVirtualAddressMap() is
 	 * unnecessary.
 	 */
-	if (VA_BITS_MIN >= 48)
+	if (VA_BITS_MIN >= 48 && !system_needs_vamap())
 		efi_novamap = true;
 
 	/* UEFI mandates support for 4 KB granularity, no need to check */