From mboxrd@z Thu Jan  1 00:00:00 1970
From: James Morse <james.morse@arm.com>
Subject: Re: [PATCH v3 01/25] arm64: hyp-stub: Implement HVC_RESET_VECTORS
 stub hypercall
Date: Tue, 21 Mar 2017 17:25:34 +0000
Message-ID: <58D1620E.30001@arm.com>
References: <20170306142458.8875-1-marc.zyngier@arm.com>
 <20170306142458.8875-2-marc.zyngier@arm.com>
 <20170321170407.GD21829@e104818-lin.cambridge.arm.com>
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Cc: cdall@linaro.org, Russell King <linux@arm.linux.org.uk>,
 kvm@vger.kernel.org, Ard Biesheuvel <ard.biesheuvel@linaro.org>,
 Marc Zyngier <marc.zyngier@arm.com>, kvmarm@lists.cs.columbia.edu,
 linux-arm-kernel@lists.infradead.org
To: Catalin Marinas <catalin.marinas@arm.com>
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Hi Catalin,

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@arm.com>
>> ---
>>  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.


Thanks,

James