Hi Shameer,
On Mon, 09 Sep 2024 16:19:54 +0100,
Shameerali Kolothum Thodi <shameerali.kolothum.thodi@xxxxxxxxxx> wrote:
>
> Hi Oliver/Sebastian,
>
> > -----Original Message-----
> > From: Oliver Upton <oliver.upton@xxxxxxxxx>
> > Sent: Wednesday, June 19, 2024 6:41 PM
> > To: kvmarm@xxxxxxxxxxxxxxx
> > Cc: Marc Zyngier <maz@xxxxxxxxxx>; James Morse
> > <james.morse@xxxxxxx>; Suzuki K Poulose <suzuki.poulose@xxxxxxx>;
> > yuzenghui <yuzenghui@xxxxxxxxxx>; kvm@xxxxxxxxxxxxxxx; Sebastian Ott
> > <sebott@xxxxxxxxxx>; Shaoqin Huang <shahuang@xxxxxxxxxx>; Eric Auger
> > <eric.auger@xxxxxxxxxx>; Oliver Upton <oliver.upton@xxxxxxxxx>
> > Subject: [PATCH v5 07/10] KVM: arm64: Treat CTR_EL0 as a VM feature ID
> > register
>
> [...]
>
> > @@ -2487,7 +2490,10 @@ static const struct sys_reg_desc sys_reg_descs[] =
> > {
> > { SYS_DESC(SYS_CCSIDR2_EL1), undef_access },
> > { SYS_DESC(SYS_SMIDR_EL1), undef_access },
> > { SYS_DESC(SYS_CSSELR_EL1), access_csselr, reset_unknown,
> > CSSELR_EL1 },
> > - { SYS_DESC(SYS_CTR_EL0), access_ctr },
> > + ID_WRITABLE(CTR_EL0, CTR_EL0_DIC_MASK |
> > + CTR_EL0_IDC_MASK |
> > + CTR_EL0_DminLine_MASK |
> > + CTR_EL0_IminLine_MASK),
>
> (Sorry if this was discussed earlier, but I couldn't locate it anywhere.)
>
> Is there a reason why we can't make the L1Ip writable as well here?
> We do have hardware that reports VIPT and PIPT for L11p.
>
> The comment here states,
> https://elixir.bootlin.com/linux/v6.11-rc7/source/arch/arm64/kernel/cpufeature.c#L489
>
> " If we have differing I-cache policies, report it as the weakest - VIPT."
>
> Does this also mean it is safe to downgrade the PIPT to VIPT for Guest as well?
It should be safe, as a PIPT CMO always does at least the same as
VIPT, and potentially more if there is aliasing.
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
