From: Marc Zyngier <maz@kernel.org>
To: Oliver Upton <oliver.upton@linux.dev>
Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
James Morse <james.morse@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Zenghui Yu <yuzenghui@huawei.com>
Subject: Re: [PATCH 07/12] arm64: Treat HCR_EL2.E2H as RES1 when ID_AA64MMFR4_EL1.E2H0 is non-zero
Date: Fri, 17 Nov 2023 12:17:25 +0000 [thread overview]
Message-ID: <86wmugzi96.wl-maz@kernel.org> (raw)
In-Reply-To: <ZVaycYt51sUWS0h+@thinky-boi>
On Fri, 17 Nov 2023 00:23:13 +0000,
Oliver Upton <oliver.upton@linux.dev> wrote:
>
> Hey Marc,
>
> On Mon, Nov 13, 2023 at 05:42:39PM +0000, Marc Zyngier wrote:
> > For CPUs that have ID_AA64MMFR4_EL1.E2H0 as non-zero, it is important
> > to avoid the boot path that sets HCR_EL2.E2H=0. Fortunately, we
> > already have this path to cope with fruity CPUs.
> >
> > Tweak init_el2 to look at ID_AA64MMFR4_EL1.E2H0 first.
> >
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > ---
> > arch/arm64/kernel/head.S | 25 +++++++++++++++++--------
> > 1 file changed, 17 insertions(+), 8 deletions(-)
> >
> > diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> > index 7b236994f0e1..5853540f7809 100644
> > --- a/arch/arm64/kernel/head.S
> > +++ b/arch/arm64/kernel/head.S
> > @@ -584,25 +584,34 @@ SYM_INNER_LABEL(init_el2, SYM_L_LOCAL)
> > mov_q x1, INIT_SCTLR_EL1_MMU_OFF
> >
> > /*
> > - * Fruity CPUs seem to have HCR_EL2.E2H set to RES1,
> > - * making it impossible to start in nVHE mode. Is that
> > - * compliant with the architecture? Absolutely not!
> > + * Compliant CPUs advertise their VHE-onlyness with
> > + * ID_AA64MMFR4_EL1.E2H0=0b111x. HCR_EL2.E2H can be
> > + * RES1 in that case.
> > + *
> > + * Fruity CPUs seem to have HCR_EL2.E2H set to RES1, but
> > + * don't advertise it (they predate this relaxation).
> > */
> > + mrs_s x0, SYS_ID_AA64MMFR4_EL1
> > + ubfx x0, x0, #ID_AA64MMFR4_EL1_E2H0_SHIFT, #ID_AA64MMFR4_EL1_E2H0_WIDTH
> > + and x0, x0, #0b1110
> > + cmp x0, #0b1110
> > + b.eq 1f
>
> Wouldn't it be more consistent with the architectural definition of
> signed feature fields to just test the sign bit in this case?
>
> Maybe like:
>
> ubfx x0, x0, #ID_AA64MMFR4_EL1_E2H0_SHIFT, #ID_AA64MMFR4_EL1_E2H0_WIDTH
> tbnz x0, #3, 1f
>
> You'll also save 8 measly bytes of text while you're at it :)
At this stage, why not try this:
tbnz x0, #(ID_AA64MMFR4_EL1_E2H0_SHIFT + ID_AA64MMFR4_EL1_E2H0_WIDTH - 1), 1f
and we save a total of 12 bytes!
M.
--
Without deviation from the norm, progress is not possible.
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next prev parent reply other threads:[~2023-11-17 12:17 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-13 17:42 [PATCH 00/12] arm64: Add support for FEAT_E2H0, or lack thereof Marc Zyngier
2023-11-13 17:42 ` [PATCH 01/12] arm64: cpufeatures: Correctly handle signed values Marc Zyngier
2023-11-17 0:45 ` Oliver Upton
2023-11-13 17:42 ` [PATCH 02/12] arm64: cpufeature: Correctly display signed override values Marc Zyngier
2023-11-17 0:46 ` Oliver Upton
2023-11-13 17:42 ` [PATCH 03/12] arm64: sysreg: Add layout for ID_AA64MMFR4_EL1 Marc Zyngier
2023-11-13 17:42 ` [PATCH 04/12] arm64: cpufeature: Add ID_AA64MMFR4_EL1 handling Marc Zyngier
2023-11-17 0:48 ` Oliver Upton
2023-11-13 17:42 ` [PATCH 05/12] arm64: cpufeature: Detect E2H0 not being implemented Marc Zyngier
2023-11-17 0:56 ` Oliver Upton
2023-11-17 12:21 ` Marc Zyngier
2023-11-13 17:42 ` [PATCH 06/12] arm64: cpufeature: Detect HCR_EL2.NV1 being RES0 Marc Zyngier
2023-11-13 17:42 ` [PATCH 07/12] arm64: Treat HCR_EL2.E2H as RES1 when ID_AA64MMFR4_EL1.E2H0 is non-zero Marc Zyngier
2023-11-17 0:23 ` Oliver Upton
2023-11-17 12:17 ` Marc Zyngier [this message]
2023-11-17 18:01 ` Oliver Upton
2023-11-13 17:42 ` [PATCH 08/12] arm64: Add override for ID_AA64MMFR4_EL1.E2H0 Marc Zyngier
2023-11-13 17:42 ` [PATCH 09/12] arm64: Add MIDR-based override infrastructure Marc Zyngier
2023-11-13 17:42 ` [PATCH 10/12] arm64: Add MIDR-based overrides for ID_AA64MMFR4_EL1.E2H0 Marc Zyngier
2023-11-13 17:42 ` [PATCH 11/12] KVM: arm64: Expose ID_AA64MMFR4_EL1 to guests Marc Zyngier
2023-11-13 17:42 ` [PATCH 12/12] KVM: arm64: Force guest's HCR_EL2.E2H RES1 when NV1 is not implemented Marc Zyngier
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