[AArch64 boot-wrapper][PATCH] aarch64: Enable FGT for EL2

We have no intention of handling FGT traps to EL3, so let EL2
play with the feature directly.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---

Notes:
    Needed to boot Linux 5.13 at EL2.

 arch/aarch64/boot.S | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/aarch64/boot.S b/arch/aarch64/boot.S
index e47cf59..fd7133d 100644
--- a/arch/aarch64/boot.S
+++ b/arch/aarch64/boot.S

@@ -54,6 +54,13 @@ _start:
 	cbz	x1, 1f
 
 	orr	x0, x0, #(1 << 34)		// TME enable
+1:
+	/* Enable FGT if present */
+	mrs	x1, id_aa64mmfr0_el1
+	ubfx	x1, x1, #56, #4
+	cbz	x1, 1f
+
+	orr	x0, x0, #(1 << 27)		// FGT enable
 1:
 #ifndef KERNEL_32
 	orr	x0, x0, #(1 << 10)		// 64-bit EL2

-- 
2.29.2


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On Mon,  3 May 2021 13:09:20 +0100
Marc Zyngier [off-list ref] wrote:

We have no intention of handling FGT traps to EL3, so let EL2
play with the feature directly.

Signed-off-by: Marc Zyngier <maz@kernel.org>

Verified the bits used against the ARM ARM. Also Trusted Firmware does
the same thing, so:

Reviewed-by: Andre Przywara <andre.przywara@arm.com>

Cheers,
Andre

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On Mon, May 03, 2021 at 01:09:20PM +0100, Marc Zyngier wrote:

We have no intention of handling FGT traps to EL3, so let EL2
play with the feature directly.

I had cooked up hacky fix after Mark Brown pointed out this could be
reason for boot failure on FVP. So,

Tested-by: Sudeep Holla <redacted>

-- 
Regards,
Sudeep

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On Mon, May 03, 2021 at 01:09:20PM +0100, Marc Zyngier wrote:

We have no intention of handling FGT traps to EL3, so let EL2
play with the feature directly.

Signed-off-by: Marc Zyngier <maz@kernel.org>

Thanks; applied.

Mark.

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