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Message-ID: <86bk2b198o.wl-maz@kernel.org>
Date: Fri, 02 Aug 2024 11:59:03 +0100
From: Marc Zyngier <maz@...nel.org>
To: Anshuman Khandual <anshuman.khandual@....com>
Cc: linux-arm-kernel@...ts.infradead.org,
Oliver Upton <oliver.upton@...ux.dev>,
James Morse <james.morse@....com>,
Suzuki K Poulose <suzuki.poulose@....com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Mark Brown <broonie@...nel.org>,
kvmarm@...ts.linux.dev,
linux-kernel@...r.kernel.org
Subject: Re: [RFC 10/10] KVM: arm64: nv: Add new HDFGRTR2_GROUP & HDFGRTR2_GROUP based FGU handling
On Fri, 02 Aug 2024 10:25:44 +0100,
Anshuman Khandual <anshuman.khandual@....com> wrote:
>
> On 8/1/24 21:33, Marc Zyngier wrote:
> > On Thu, 01 Aug 2024 11:46:22 +0100,
> > Anshuman Khandual <anshuman.khandual@....com> wrote:
[...]
> >> + SR_FGT(SYS_SPMACCESSR_EL1, HDFGRTR2, nSPMACCESSR_EL1, 0),
> >
> > This (and I take it most of the stuff here) is also gated by
> > MDCR_EL2.SPM, which is a coarse grained trap. That needs to be
> > described as well. For every new register that you add here.
>
> I did not find a SPM field in MDCR_EL2 either in latest ARM ARM or in
> the latest XML. But as per current HDFGRTR2_EL2 description the field
> nSPMACCESSR_EL1 is gated by FEAT_SPMU feature, which is being checked
> via ID_AA64DFR1_EL1.PMU when required. So could you please give some
> more details.
I misspelled it. It is MDCR_EL2.EnSPM.
And you are completely missing the point. It is not about
HDFGRTR2_EL2, but about SPMACCESSR_EL1 (and all its little friends).
To convince yourself, just look at the pseudocode for SPMACCESSR_EL1,
limited to an EL1 access:
elsif PSTATE.EL == EL1 then
if HaveEL(EL3) && EL3SDDUndefPriority() && MDCR_EL3.EnPM2 == '0' then
UNDEFINED;
elsif EL2Enabled() && IsFeatureImplemented(FEAT_FGT2) && ((HaveEL(EL3) && SCR_EL3.FGTEn2 == '0') || HDFGRTR2_EL2.nSPMACCESSR_EL1 == '0') then
AArch64.SystemAccessTrap(EL2, 0x18);
elsif EL2Enabled() && MDCR_EL2.EnSPM == '0' then
AArch64.SystemAccessTrap(EL2, 0x18);
elsif HaveEL(EL3) && MDCR_EL3.EnPM2 == '0' then
if EL3SDDUndef() then
UNDEFINED;
else
AArch64.SystemAccessTrap(EL3, 0x18);
elsif EffectiveHCR_EL2_NVx() IN {'111'} then
X[t, 64] = NVMem[0x8E8];
else
X[t, 64] = SPMACCESSR_EL1;
Can you spot the *TWO* conditions where we take an exception to EL2
with 0x18 as the EC?
- One is when HDFGxTR2_EL2.nSPMACCESSR_EL1 == '0': that's a fine
grained trap.
- The other is when MDCR_EL2.EnSPM == '0': that's a coarse grained
trap.
Both conditions need to be captured in the various tables in this
file, for each and every register that you describe.
[...]
> > Now, the main issues are that:
> >
> > - you're missing the coarse grained trapping for all the stuff you
> > have just added. It's not a huge amount of work, but you need, for
> > each register, to describe what traps apply to it. The fine grained
> > stuff is most, but not all of it. There should be enough of it
> > already to guide you through it.
>
> Coarse grained trapping for FEAT_FGT2 based fine grained registers ?
Not for FEAT_FGT2. For the registers that FEAT_FGT2 traps. Can you see
the difference?
> Afraid, did not understand this. Could you please give some pointers
> on similar existing code.
See above. And if you want some example, just took at the file you are
patching already. Look at how MDCR_EL2 conditions the trapping of all
the debug, PMU, AMU registers, for example. There is no shortage of
them.
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
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