On 21/03/17 17:37, Marc Zyngier wrote: > On 21/03/17 17:25, James Morse wrote: >> On 21/03/17 17:04, Catalin Marinas wrote: >>> On Mon, Mar 06, 2017 at 02:24:34PM +0000, Marc Zyngier wrote: >>>> 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 <marc.zyngier@xxxxxxx> >>>> --- >>>> arch/arm64/include/asm/virt.h | 9 +++++++++ >>>> arch/arm64/kernel/hyp-stub.S | 13 ++++++++++++- >>>> 2 files changed, 21 insertions(+), 1 deletion(-) >>> [...] >>>> +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
