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To: Richard Henderson <richard.henderson@linaro.org>
Subject: Re: [PATCH v2 3/5] target/arm: Handle trapping to EL2 of AArch32 VMRS
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Date: Mon, 02 Dec 2019 16:45:34 +0000
From: Marc Zyngier <maz@kernel.org>
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On 2019-12-02 15:35, Richard Henderson wrote:
> On 12/1/19 12:20 PM, Marc Zyngier wrote:
>> HCR_EL2.TID3 requires that AArch32 reads of MVFR[012] are trapped to
>> EL2, and HCR_EL2.TID0 does the same for reads of FPSID.
>> In order to handle this, introduce a new TCG helper function that
>> checks for these control bits before executing the VMRC instruction.
>>
>> Tested with a hacked-up version of KVM/arm64 that sets the control
>> bits for 32bit guests.
>>
>> Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
>> Signed-off-by: Marc Zyngier <maz@kernel.org>
>> ---
>>  target/arm/helper-a64.h        |  2 ++
>>  target/arm/translate-vfp.inc.c | 18 +++++++++++++++---
>>  target/arm/vfp_helper.c        | 29 +++++++++++++++++++++++++++++
>>  3 files changed, 46 insertions(+), 3 deletions(-)
>
> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
>
> Annoying that there's a bug in the manual -- FPSID is listed as group 
> 0 in
> plenty of places, except in the pseudo-code for Accessing the FPSID
> which uses TID3.

Are you sure? I'm looking at DDI0487E_a, and the pseudo-code for
AArch32.CheckAdvSIMDOrFPRegisterTraps has this check:

<quote>
if (tid0 == '1' && reg == '0000')                           // FPSID
   || (tid3 == '1' && reg IN {'0101', '0110', '0111'}) then  // MVFRx
     if ELUsingAArch32(EL2) then
       AArch32.SystemAccessTrap(M32_Hyp, 0x8);    // 
Exception_AdvSIMDFPAccessTrap
     else
       AArch64.AArch32SystemAccessTrap(EL2, 0x8); // 
Exception_AdvSIMDFPAccessTrap
</quote>

which seems to do the right thing. Or have you spotted a discrepancy
somewhere else (which would be oh-so-surprising...)?

Thanks,

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