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Date: Sat, 30 May 2015 10:30:33 +0800
From: Shannon Zhao <zhaoshenglong@huawei.com>
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Subject: Re: [Qemu-devel] [PATCH] Use Aff1 with mpidr
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To: Pavel Fedin <p.fedin@samsung.com>, 'Igor Mammedov' <imammedo@redhat.com>
Cc: peter.maydell@linaro.org, qemu-devel@nongnu.org, 'Ashok Kumar' <ashoks@broadcom.com>, 'Shlomo Pongratz' <shlomo.pongratz@huawei.com>



On 2015/5/30 1:37, Pavel Fedin wrote:
>  Hi!
> 
>> Well KVM side should be fixed instead of driving us along wrong route.
> 
>  I have studied the question a bit more, and i discovered that MPIDR access on ARM is not
> trapped by KVM. And guest would always get the same value as host would. Theoretically you

Yes, it doesn't trap but there is one register "vmpidr_el2" which is
used for virtualization. When guest reads mpidr, it will get the value
of vmpidr_el2. And when context switching, hyp will restore the value of
vmpidr_el2 and the value is got from MPIDR_EL1 which is set by
reset_mpidr().

hyp.s:

.macro restore_sysregs // x2: base address for cpu context
	// x3: tmp register
	add	x3, x2, #CPU_SYSREG_OFFSET(MPIDR_EL1)
----cut----
	msr	vmpidr_el2,	x4
----cut----
.endm


-- 
Shannon