From b7e5aee0a36487d6205c1633add25fd430d3b6d7 Mon Sep 17 00:00:00 2001 From: "Kyle J. Temkin" Date: Thu, 28 Apr 2016 13:14:07 -0400 Subject: [PATCH] xen/arm64: ensure that the correct SP is used for exceptions The ARMv8 architecture has a SPSel ("stack pointer selection") machine register that allows us to determine which exception level's stack pointer is loaded when an exception occurs. As we don't want to use the non-privileged SP_EL0 stack pointer -- or even assume that SP_EL0 points to a valid address in the hypervisor context-- we'll need to ensure that our EL2 code sets the SPSel to SP_ELn mode, so exceptions that trap to EL2 use the EL2 stack pointer. This corrects an issue that can manifest as a hang-on-IRQ on some arm64 cores if the firmware/bootloader has previously initialized SPSel to 0; in which case Xen's exceptions will incorrectly use an invalid SP_EL0, and will endlessly spin on the synchronous abort handler. Signed-off-by: Kyle Temkin Signed-off-by: Stefano Stabellini Reviewed-by: Julien Grall --- xen/arch/arm/arm64/head.S | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S index 946e2c93e9..d5831f22b0 100644 --- a/xen/arch/arm/arm64/head.S +++ b/xen/arch/arm/arm64/head.S @@ -361,6 +361,11 @@ skip_bss: ldr x0, =(HSCTLR_BASE) msr SCTLR_EL2, x0 + /* Ensure that any exceptions encountered at EL2 + * are handled using the EL2 stack pointer, rather + * than SP_EL0. */ + msr spsel, #1 + /* Rebuild the boot pagetable's first-level entries. The structure * is described in mm.c. * -- 2.30.2