[PATCH v3 01/25] arm64: hyp-stub: Implement HVC_RESET_VECTORS stub hypercall

On 21/03/17 17:37, Marc Zyngier wrote:

On 21/03/17 17:25, James Morse wrote:

quoted

On 21/03/17 17:04, Catalin Marinas wrote:

quoted

On Mon, Mar 06, 2017 at 02:24:34PM +0000, Marc Zyngier wrote:

quoted

Let's define a new stub hypercall that resets the HYP configuration
to its default: hyp-stub vectors, and MMU disabled.

Of course, for the hyp-stub itself, this is a trivial no-op.
Hypervisors will have a bit more work to do.

Signed-off-by: Marc Zyngier <redacted>
---
 arch/arm64/include/asm/virt.h |  9 +++++++++
 arch/arm64/kernel/hyp-stub.S  | 13 ++++++++++++-
 2 files changed, 21 insertions(+), 1 deletion(-)

[...]

quoted

+ENTRY(__hyp_reset_vectors)
+	str	lr, [sp, #-16]!
+	mov	x0, #HVC_RESET_VECTORS
+	hvc	#0
+	ldr	lr, [sp], #16
+	ret
+ENDPROC(__hyp_reset_vectors)

Why do we need to specifically preserve lr across the hvc call? Is it
corrupted by the EL2 code (if yes, are other caller-saved registers that
need preserving)? I don't see something similar in the arch/arm code.

Kexec on arm64 needed a register to clobber in the hyp-stub's el1_sync code. We
wanted to preserve all the registers so soft_restart() could look more like a
function call.

I don't think we need this anymore. Once we enter __cpu_soft_restart(),
there is no turning back. Or am I missing something else?

My recollection of the history may be wrong: but we needed to mess with esr_el2
before we know its a soft_restart() call, at which point we didn't want to
clobber the registers. This was the strange use of x18 in kexec.


James