arm64: sdei: Add trampoline code for remapping the kernel

When CONFIG_UNMAP_KERNEL_AT_EL0 is set the SDEI entry point and the rest
of the kernel may be unmapped when we take an event. If this may be the
case, use an entry trampoline that can switch to the kernel page tables.

We can't use the provided PSTATE to determine whether to switch page
tables as we may have interrupted the kernel's entry trampoline, (or a
normal-priority event that interrupted the kernel's entry trampoline).
Instead test for a user ASID in ttbr1_el1.

Save a value in regs->addr_limit to indicate whether we need to restore
the original ASID when returning from this event. This value is only used
by do_page_fault(), which we don't call with the SDEI regs.

Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/arch/arm64/include/asm/sdei.h b/arch/arm64/include/asm/sdei.h
index d58a31ab525a..e073e6886685 100644
--- a/arch/arm64/include/asm/sdei.h
+++ b/arch/arm64/include/asm/sdei.h
@@ -23,6 +23,12 @@ extern unsigned long sdei_exit_mode;
 asmlinkage void __sdei_asm_handler(unsigned long event_num, unsigned long arg,
 				   unsigned long pc, unsigned long pstate);
 
+/* and its CONFIG_UNMAP_KERNEL_AT_EL0 trampoline */
+asmlinkage void __sdei_asm_entry_trampoline(unsigned long event_num,
+						   unsigned long arg,
+						   unsigned long pc,
+						   unsigned long pstate);
+
 /*
  * The above entry point does the minimum to call C code. This function does
  * anything else, before calling the driver.