From mboxrd@z Thu Jan  1 00:00:00 1970
From: Marc Zyngier <marc.zyngier@arm.com>
Subject: Re: [PATCH 21/27] arm64/sve: KVM: Prevent guests from using SVE
Date: Wed, 16 Aug 2017 12:22:47 +0100
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Cc: linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org, libc-alpha@sourceware.org, Ard Biesheuvel <ard.biesheuvel@linaro.org>, Szabolcs Nagy <szabolcs.nagy@arm.com>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will.deacon@arm.com>, Richard Sandiford <richard.sandiford@arm.com>, kvmarm@lists.cs.columbia.edu, Christoffer Dall <christoffer.dall@linaro.org>

On 16/08/17 12:20, Marc Zyngier wrote:
> On 16/08/17 11:50, Dave Martin wrote:
>> On Tue, Aug 15, 2017 at 05:33:15PM +0100, Marc Zyngier wrote:
>>> On 09/08/17 13:05, Dave Martin wrote:
>>>> Until KVM has full SVE support, guests must not be allowed to
>>>> execute SVE instructions.
>>>>
>>>> This patch enables the necessary traps, and also ensures that the
>>>> traps are disabled again on exit from the guest so that the host
>>>> can still use SVE if it wants to.
>>>>
>>>> Signed-off-by: Dave Martin <Dave.Martin@arm.com>
>>>> ---
>>>>  arch/arm64/include/asm/kvm_arm.h | 3 ++-
>>>>  arch/arm64/kvm/hyp/switch.c      | 6 +++---
>>>>  2 files changed, 5 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h
>>>> index dbf0537..8a19651 100644
>>>> --- a/arch/arm64/include/asm/kvm_arm.h
>>>> +++ b/arch/arm64/include/asm/kvm_arm.h
>>>> @@ -186,7 +186,7 @@
>>>>  #define CPTR_EL2_TTA	(1 << 20)
>>>>  #define CPTR_EL2_TFP	(1 << CPTR_EL2_TFP_SHIFT)
>>>>  #define CPTR_EL2_TZ	(1 << 8)
>>>> -#define CPTR_EL2_DEFAULT	0x000033ff
>>>> +#define CPTR_EL2_DEFAULT	(0x000033ff & ~CPTR_EL2_TZ)
>>>
>>> I must say I'm not overly fond of this construct. I'd rather introduce a
>>> RES1 field that matches the v8.2 description, instead of this ugly
>>> constant and something that clears it.
>>
>> Sorry, I don't get your meaning here.  v8.2 neither immediately predates
>> or postdates SVE.  
> 
> The ARMv8 ARM (DDI406B_a, D7.2.19) says otherwise. This bit is only

Of course, the days of the ARMv7 ARM are still haunting me. This should
read DDI487B_a.

Apologies for the confusion.

	M.
-- 
Jazz is not dead. It just smells funny...