From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Morse Subject: Re: [PATCH v3 01/25] arm64: hyp-stub: Implement HVC_RESET_VECTORS stub hypercall Date: Tue, 21 Mar 2017 17:41:54 +0000 Message-ID: <58D165E2.7050501@arm.com> References: <20170306142458.8875-1-marc.zyngier@arm.com> <20170306142458.8875-2-marc.zyngier@arm.com> <20170321170407.GD21829@e104818-lin.cambridge.arm.com> <58D1620E.30001@arm.com> <0cce34c1-cb6f-0ba3-ac98-c0a0e986dc86@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: cdall@linaro.org, Russell King , kvm@vger.kernel.org, Ard Biesheuvel , Catalin Marinas , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org To: Marc Zyngier Return-path: In-Reply-To: <0cce34c1-cb6f-0ba3-ac98-c0a0e986dc86@arm.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu List-Id: kvm.vger.kernel.org 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 >>>> --- >>>> 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