From: Quentin Perret <qperret@google.com>
To: Marc Zyngier <maz@kernel.org>
Cc: catalin.marinas@arm.com, james.morse@arm.com,
julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com,
android-kvm@google.com, seanjc@google.com, mate.toth-pal@arm.com,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, kernel-team@android.com,
kvmarm@lists.cs.columbia.edu, tabba@google.com, ardb@kernel.org,
mark.rutland@arm.com, dbrazdil@google.com
Subject: Re: [PATCH 2/3] KVM: arm64: Generate final CTR_EL0 value when running in Protected mode
Date: Mon, 22 Mar 2021 17:40:40 +0000 [thread overview]
Message-ID: <YFjWmHerKk7+9d7N@google.com> (raw)
In-Reply-To: <20210322164828.800662-3-maz@kernel.org>
Hey Marc,
On Monday 22 Mar 2021 at 16:48:27 (+0000), Marc Zyngier wrote:
> In protected mode, late CPUs are not allowed to boot (enforced by
> the PSCI relay). We can thus specialise the read_ctr macro to
> always return a pre-computed, sanitised value.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
> arch/arm64/include/asm/assembler.h | 9 +++++++++
> arch/arm64/kernel/image-vars.h | 1 +
> arch/arm64/kvm/va_layout.c | 7 +++++++
> 3 files changed, 17 insertions(+)
>
> diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
> index fb651c1f26e9..1a4cee7eb3c9 100644
> --- a/arch/arm64/include/asm/assembler.h
> +++ b/arch/arm64/include/asm/assembler.h
> @@ -270,12 +270,21 @@ alternative_endif
> * provide the system wide safe value from arm64_ftr_reg_ctrel0.sys_val
> */
> .macro read_ctr, reg
> +#ifndef __KVM_NVHE_HYPERVISOR__
> alternative_if_not ARM64_MISMATCHED_CACHE_TYPE
> mrs \reg, ctr_el0 // read CTR
> nop
> alternative_else
> ldr_l \reg, arm64_ftr_reg_ctrel0 + ARM64_FTR_SYSVAL
> alternative_endif
> +#else
> +alternative_cb kvm_compute_final_ctr_el0
> + movz \reg, #0
> + movk \reg, #0, lsl #16
> + movk \reg, #0, lsl #32
> + movk \reg, #0, lsl #48
> +alternative_cb_end
> +#endif
> .endm
So, FWIW, if we wanted to make _this_ macro BUG in non-protected mode
(and drop patch 01), I think we could do something like:
alternative_cb kvm_compute_final_ctr_el0
movz \reg, #0
ASM_BUG()
nop
nop
alternative_cb_end
and then make kvm_compute_final_ctr_el0() check that we're in protected
mode before patching. That would be marginally better as that would
cover _all_ users of read_ctr and not just __flush_dcache_area, but that
first movz is a bit yuck (but necessary to keep generate_mov_q() happy I
think?), so I'll leave the decision to you.
No objection from me for the current implementation, and if you decide to
go with it:
Reviewed-by: Quentin Perret <qperret@google.com>
Thanks,
Quentin
next prev parent reply other threads:[~2021-03-22 17:41 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-22 16:48 [PATCH 0/3] KVM:arm64: Proposed host stage-2 improvements Marc Zyngier
2021-03-22 16:48 ` [PATCH 1/3] KVM: arm64: Constraint KVM's own __flush_dcache_area to protectected mode Marc Zyngier
2021-03-22 16:48 ` [PATCH 2/3] KVM: arm64: Generate final CTR_EL0 value when running in Protected mode Marc Zyngier
2021-03-22 17:40 ` Quentin Perret [this message]
2021-03-22 18:37 ` Marc Zyngier
2021-03-23 9:47 ` Quentin Perret
2021-03-22 16:48 ` [PATCH 3/3] KVM: arm64: Drop the CPU_FTR_REG_HYP_COPY infrastructure Marc Zyngier
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