linux-kernel - Re: [PATCH v2 05/21] arm64: KVM: VHE: Turn VTCR

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Date:	Mon, 1 Feb 2016 16:38:14 +0100
From:	Christoffer Dall <christoffer.dall@...aro.org>
To:	Marc Zyngier <marc.zyngier@....com>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, kvmarm@...ts.cs.columbia.edu
Subject: Re: [PATCH v2 05/21] arm64: KVM: VHE: Turn VTCR_EL2 setup into a
 reusable macro

On Mon, Feb 01, 2016 at 02:21:57PM +0000, Marc Zyngier wrote:
> On 01/02/16 13:13, Christoffer Dall wrote:
> > On Mon, Jan 25, 2016 at 03:53:39PM +0000, Marc Zyngier wrote:
> >> On a VHE-capable system, there is no point in setting VTCR_EL2
> >> at KVM init time. We can perfectly set it up when the kernel
> >> boots, removing the need for a more complicated configuration.
> > 
> > what's the complicated configuration which is avoided?
> 
> With VHE, there is no hyp-init at all, so what we avoid is a weird init
> sequence where we have to execute part of this hyp-init, but not all of it.
> 
> >>
> >> In order to allow this, turn VTCR_EL2 setup into a macro that
> >> we'll be able to reuse at boot time.
> >>
> >> Signed-off-by: Marc Zyngier <marc.zyngier@....com>
> >> ---
> >>  arch/arm64/include/asm/kvm_mmu.h | 23 +++++++++++++++++++++++
> >>  arch/arm64/kvm/hyp-init.S        | 18 +-----------------
> >>  2 files changed, 24 insertions(+), 17 deletions(-)
> >>
> >> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
> >> index 7364339..d3e6d7b 100644
> >> --- a/arch/arm64/include/asm/kvm_mmu.h
> >> +++ b/arch/arm64/include/asm/kvm_mmu.h
> >> @@ -56,6 +56,29 @@
> >>  
> >>  #ifdef __ASSEMBLY__
> >>  
> >> +#include <asm/kvm_arm.h>
> >> +
> >> +.macro setup_vtcr tmp1, tmp2
> >> +	mov	\tmp1, #(VTCR_EL2_FLAGS & 0xffff)
> >> +	movk	\tmp1, #(VTCR_EL2_FLAGS >> 16), lsl #16
> >> +	/*
> >> +	 * Read the PARange bits from ID_AA64MMFR0_EL1 and set the PS bits in
> >> +	 * VTCR_EL2.
> >> +	 */
> >> +	mrs	\tmp2, id_aa64mmfr0_el1
> >> +	bfi	\tmp1, \tmp2, #16, #3
> >> +	/*
> >> +	 * Read the VMIDBits bits from ID_AA64MMFR1_EL1 and set the VS bit in
> >> +	 * VTCR_EL2.
> >> +	 */
> >> +	mrs	\tmp2, ID_AA64MMFR1_EL1
> >> +	ubfx	\tmp2, \tmp2, #5, #1
> >> +	lsl	\tmp2, \tmp2, #VTCR_EL2_VS
> >> +	orr	\tmp1, \tmp1, \tmp2
> >> +
> >> +	msr	vtcr_el2, \tmp1
> >> +	isb
> >> +.endm
> > 
> > this feels like an awful lot of code in a header file.
> 
> interrupt_head.S respectfully disagrees with you ;-).
> 
> > Is it crazy to imagine wanting to have different T0SZ for different VMs
> > in the future?  In that case, the T0SZ stuff should stay in KVM...
> 
> That's a rather compelling argument indeed. I'll see if I can turn the
> thing around in a slightly nicer way. How about moving it out of
> hyp-init.S altogether, and into C code?

That sounds better to me.

Thanks,
-Christoffer