Re: [Xen-devel] [PATCH v3 03/19] xen/arm: Set and restore HCR_EL2 register for each vCPU separately

[Julien Grall <julien.grall@xxxxxxx>]

Hi Wei,

On 31/03/17 14:07, Wei Chen wrote:
> Different domains may have different HCR_EL2 flags. For example, the
> 64-bit domain needs HCR_RW flag but the 32-bit does not need it. So
> we give each domain a default HCR_EL2 value and save it in the vCPU's
> context.
>
> HCR_EL2 register has only one bit can be updated automatically without
> explicit write (HCR_VSE). But we haven't used this bit currently, so
> we can consider that the HCR_EL2 register will not be modified while
> the guest is running. So save the HCR_EL2 while guest exiting to
> hypervisor is not neccessary. We just have to restore this register for
> each vCPU while context switching.
>
> The p2m_restore_state which will be invoked in context switch progress
> has included the writing of HCR_EL2 already. It updates the HCR_EL2.RW
> bit to tell the hardware how to interpret the stage-1 page table as the
> encodings are different between AArch64 and AArch32. We can reuse this
> write to restore the HCR_EL2 for each vCPU. Of course, the value of each
> vCPU's HCR_EL2 should be adjusted to have proper HCR_EL2.RW bit in this
> function. In the later patch of this series, we will set the HCR_EL2.RW
> for each vCPU while the domain is creating.
>
> Signed-off-by: wei chen <Wei.Chen@xxxxxxx>
Reviewed-by: Julien Grall <julien.grall@xxxxxxx>

Cheers,

--
Julien Grall

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