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From: Alexandru Elisei <alexandru.elisei@arm.com>
To: Marc Zyngier <maz@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org
Cc: kernel-team@android.com, Andre Przywara <andre.przywara@arm.com>,
	Dave Martin <Dave.Martin@arm.com>,
	George Cherian <gcherian@marvell.com>,
	"Zengtao \(B\)" <prime.zeng@hisilicon.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>
Subject: Re: [PATCH v2 06/17] KVM: arm64: Introduce accessor for ctxt->sys_reg
Date: Fri, 26 Jun 2020 16:39:52 +0100	[thread overview]
Message-ID: <a9c3a43e-7850-e74d-5383-905885721ab4@arm.com> (raw)
In-Reply-To: <20200615132719.1932408-7-maz@kernel.org>

Hi,

On 6/15/20 2:27 PM, Marc Zyngier wrote:
> In order to allow the disintegration of the per-vcpu sysreg array,
> let's introduce a new helper (ctxt_sys_reg()) that returns the
> in-memory copy of a system register, picked from a given context.
>
> __vcpu_sys_reg() is rewritten to use this helper.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  arch/arm64/include/asm/kvm_host.h | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index e7fd03271e52..5314399944e7 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -405,12 +405,17 @@ struct kvm_vcpu_arch {
>  #define vcpu_gp_regs(v)		(&(v)->arch.ctxt.gp_regs)
>  
>  /*
> - * Only use __vcpu_sys_reg if you know you want the memory backed version of a
> - * register, and not the one most recently accessed by a running VCPU.  For
> - * example, for userspace access or for system registers that are never context
> - * switched, but only emulated.
> + * Only use __vcpu_sys_reg/ctxt_sys_reg if you know you want the
> + * memory backed version of a register, and not the one most recently
> + * accessed by a running VCPU.  For example, for userspace access or
> + * for system registers that are never context switched, but only
> + * emulated.
>   */
> -#define __vcpu_sys_reg(v,r)	((v)->arch.ctxt.sys_regs[(r)])
> +#define __ctxt_sys_reg(c,r)	(&(c)->sys_regs[(r)])
> +
> +#define ctxt_sys_reg(c,r)	(*__ctxt_sys_reg(c,r))
> +
> +#define __vcpu_sys_reg(v,r)	(ctxt_sys_reg(&(v)->arch.ctxt, (r)))

This is confusing - __vcpu_sys_reg() returns the value, but __ctxt_sys_reg()
return a pointer to the value. Because of that, I made the mistake of thinking
that __vcpu_sys_reg() returns a pointer when reviewing the next patch in the
series, and I got really worried that stuff was seriously broken (it was not).

I'm not sure what the reasonable solution is, or even if there is one.

Some thoughts: we could have just one macro, ctxt_sys_reg() and dereference that
when we want the value; we could keep both and swap the macro definitions; or we
could encode the fact that a macro returns a pointer in the macro name (so we
would end up with __ctxt_sys_reg() -> __ctxt_sys_regp() and ctxt_sys_reg ->
__ctxt_sys_reg()).

What do you think?

Thanks,
Alex
>  
>  u64 vcpu_read_sys_reg(const struct kvm_vcpu *vcpu, int reg);
>  void vcpu_write_sys_reg(struct kvm_vcpu *vcpu, u64 val, int reg);
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  reply	other threads:[~2020-06-26 15:39 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-15 13:27 [PATCH v2 00/17] KVM: arm64: Preliminary NV patches Marc Zyngier
2020-06-15 13:27 ` [PATCH v2 01/17] KVM: arm64: Factor out stage 2 page table data from struct kvm Marc Zyngier
2020-06-16 15:59   ` Alexandru Elisei
2020-06-16 16:18     ` Marc Zyngier
2020-06-17 12:58       ` Alexandru Elisei
2020-06-25 12:19       ` Alexandru Elisei
2020-07-06 12:17         ` Marc Zyngier
2020-07-06 15:49           ` Alexandru Elisei
2020-06-17 12:40   ` Marc Zyngier
2020-06-25 12:49   ` Alexandru Elisei
2020-07-13  9:47   ` Andrew Scull
2020-07-13 14:20     ` Marc Zyngier
2020-06-15 13:27 ` [PATCH v2 02/17] arm64: Detect the ARMv8.4 TTL feature Marc Zyngier
2020-06-15 13:27 ` [PATCH v2 03/17] arm64: Document SW reserved PTE/PMD bits in Stage-2 descriptors Marc Zyngier
2020-06-15 13:27 ` [PATCH v2 04/17] arm64: Add level-hinted TLB invalidation helper Marc Zyngier
2020-06-25 16:24   ` Alexandru Elisei
2020-06-15 13:27 ` [PATCH v2 05/17] KVM: arm64: Use TTL hint in when invalidating stage-2 translations Marc Zyngier
2020-06-26 13:14   ` Alexandru Elisei
2020-06-15 13:27 ` [PATCH v2 06/17] KVM: arm64: Introduce accessor for ctxt->sys_reg Marc Zyngier
2020-06-26 15:39   ` Alexandru Elisei [this message]
2020-07-06 12:15     ` Marc Zyngier
2020-07-06 12:35       ` Alexandru Elisei
2020-06-15 13:27 ` [PATCH v2 07/17] KVM: arm64: hyp: Use ctxt_sys_reg/__vcpu_sys_reg instead of raw sys_regs access Marc Zyngier
2020-06-15 13:27 ` [PATCH v2 08/17] KVM: arm64: sve: Use __vcpu_sys_reg() " Marc Zyngier
2020-06-15 13:27 ` [PATCH v2 09/17] KVM: arm64: pauth: Use ctxt_sys_reg() " Marc Zyngier
2020-06-15 13:27 ` [PATCH v2 10/17] KVM: arm64: debug: " Marc Zyngier
2020-06-15 13:27 ` [PATCH v2 11/17] KVM: arm64: Make struct kvm_regs userspace-only Marc Zyngier
2020-06-15 13:27 ` [PATCH v2 12/17] KVM: arm64: Move ELR_EL1 to the system register array Marc Zyngier
2020-06-15 13:27 ` [PATCH v2 13/17] KVM: arm64: Move SP_EL1 " Marc Zyngier
2020-06-15 13:27 ` [PATCH v2 14/17] KVM: arm64: Disintegrate SPSR array Marc Zyngier
2020-06-15 13:27 ` [PATCH v2 15/17] KVM: arm64: Move SPSR_EL1 to the system register array Marc Zyngier
2020-06-15 13:27 ` [PATCH v2 16/17] KVM: arm64: timers: Rename kvm_timer_sync_hwstate to kvm_timer_sync_user Marc Zyngier
2020-06-15 13:27 ` [PATCH v2 17/17] KVM: arm64: timers: Move timer registers to the sys_regs file Marc Zyngier

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