arm64: entry: split SDEI entry

We'd like to keep all the entry sequencing in entry-common.c, as this
will allow us to ensure this is consistent, and free from any unsound
instrumentation.

Currently __sdei_handler() performs the NMI entry/exit sequences in
sdei.c. Let's split the low-level entry sequence from the event
handling, moving the former to entry-common.c and keeping the latter in
sdei.c. The event handling function is renamed to do_sdei_event(),
matching the do_${FOO}() pattern used for other exception handlers.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20210607094624.34689-18-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

1 files changed, 37 insertions, 0 deletions

diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
index efe95edf10c0..1b32ca3848f5 100644
--- a/arch/arm64/kernel/entry-common.c
+++ b/arch/arm64/kernel/entry-common.c
@@ -20,6 +20,7 @@
 #include <asm/kprobes.h>
 #include <asm/mmu.h>
 #include <asm/processor.h>
+#include <asm/sdei.h>
 #include <asm/stacktrace.h>
 #include <asm/sysreg.h>
 #include <asm/system_misc.h>
@@ -710,3 +711,39 @@ asmlinkage void noinstr handle_bad_stack(struct pt_regs *regs)
 	panic_bad_stack(regs, esr, far);
 }
 #endif /* CONFIG_VMAP_STACK */
+
+#ifdef CONFIG_ARM_SDE_INTERFACE
+asmlinkage noinstr unsigned long
+__sdei_handler(struct pt_regs *regs, struct sdei_registered_event *arg)
+{
+	unsigned long ret;
+
+	/*
+	 * We didn't take an exception to get here, so the HW hasn't
+	 * set/cleared bits in PSTATE that we may rely on.
+	 *
+	 * The original SDEI spec (ARM DEN 0054A) can be read ambiguously as to
+	 * whether PSTATE bits are inherited unchanged or generated from
+	 * scratch, and the TF-A implementation always clears PAN and always
+	 * clears UAO. There are no other known implementations.
+	 *
+	 * Subsequent revisions (ARM DEN 0054B) follow the usual rules for how
+	 * PSTATE is modified upon architectural exceptions, and so PAN is
+	 * either inherited or set per SCTLR_ELx.SPAN, and UAO is always
+	 * cleared.
+	 *
+	 * We must explicitly reset PAN to the expected state, including
+	 * clearing it when the host isn't using it, in case a VM had it set.
+	 */
+	if (system_uses_hw_pan())
+		set_pstate_pan(1);
+	else if (cpu_has_pan())
+		set_pstate_pan(0);
+
+	arm64_enter_nmi(regs);
+	ret = do_sdei_event(regs, arg);
+	arm64_exit_nmi(regs);
+
+	return ret;
+}
+#endif /* CONFIG_ARM_SDE_INTERFACE */