From: Marc Zyngier <maz@kernel.org>
To: James Morse <james.morse@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
kvm@vger.kernel.org, Suzuki K Poulose <suzuki.poulose@arm.com>,
Jintack Lim <jintack@cs.columbia.edu>,
Andre Przywara <andre.przywara@arm.com>,
Christoffer Dall <christoffer.dall@arm.com>,
kvmarm@lists.cs.columbia.edu, Will Deacon <will@kernel.org>,
George Cherian <gcherian@marvell.com>,
Julien Thierry <julien.thierry.kdev@gmail.com>,
"Zengtao \(B\)" <prime.zeng@hisilicon.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Alexandru Elisei <alexandru.elisei@arm.com>,
Dave Martin <Dave.Martin@arm.com>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 03/26] KVM: arm64: Factor out stage 2 page table data from struct kvm
Date: Wed, 6 May 2020 10:30:29 +0100 [thread overview]
Message-ID: <20200506103029.4f6ca0d3@why> (raw)
In-Reply-To: <86o8r2tg83.wl-maz@kernel.org>
On Tue, 05 May 2020 18:59:56 +0100
Marc Zyngier <maz@kernel.org> wrote:
Hi James,
> > But accessing VTCR is why the stage2_dissolve_p?d() stuff still
> > needs the kvm pointer, hence the backreference... it might be neater
> > to push the vtcr properties into kvm_s2_mmu that way you could drop
> > the kvm backref, and only things that take vm-wide locks would need
> > the kvm pointer. But I don't think it matters.
>
> That's an interesting consideration. I'll have a look.
So I went back on forth on this (the joys of not sleeping), and decided
to keep the host's VTCR_EL2 where it is today (in the kvm structure).
Two reasons for this:
- This field is part of the host configuration. Moving it to the S2 MMU
structure muddies the waters a bit once you start nesting, as this
structure really describes an inner guest context. It has its own
associated VTCR, which lives in the sysreg file, and it becomes a bit
confusing to look at a kvm_s2_mmu structure in isolation and wonder
whether this field is directly related to the PTs in this structure,
or to something else.
- It duplicates state. If there is one thing I have learned over the
past years, it is that you should keep a given state in one single
place at all times. Granted, VTCR doesn't change over the lifetime of
the guest, but still.
I guess the one thing that would push me to the other side of the
debate is if we can show that the amount of pointer chasing generated
by the mmu->kvm->vtcr dance is causing actual performance issues. So
far, I haven't measured such an impact.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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next prev parent reply other threads:[~2020-05-06 9:30 UTC|newest]
Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-22 12:00 [PATCH 00/26] KVM: arm64: Preliminary NV patches Marc Zyngier
2020-04-22 12:00 ` [PATCH 01/26] KVM: arm64: Check advertised Stage-2 page size capability Marc Zyngier
2020-04-22 13:40 ` Suzuki K Poulose
2020-04-22 14:07 ` Marc Zyngier
2020-04-22 14:14 ` Suzuki K Poulose
2020-05-07 11:42 ` Alexandru Elisei
2020-04-22 12:00 ` [PATCH 02/26] KVM: arm64: Move __load_guest_stage2 to kvm_mmu.h Marc Zyngier
2020-04-22 13:51 ` Suzuki K Poulose
2020-04-22 13:59 ` Marc Zyngier
2020-04-22 12:00 ` [PATCH 03/26] KVM: arm64: Factor out stage 2 page table data from struct kvm Marc Zyngier
2020-05-05 15:26 ` Andrew Scull
2020-05-05 16:32 ` Marc Zyngier
2020-05-05 17:23 ` Andrew Scull
2020-05-05 18:10 ` Marc Zyngier
2020-05-05 16:03 ` James Morse
2020-05-05 17:59 ` Marc Zyngier
2020-05-06 9:30 ` Marc Zyngier [this message]
2020-05-11 16:38 ` Alexandru Elisei
2020-05-12 11:17 ` James Morse
2020-05-12 15:47 ` Alexandru Elisei
2020-05-12 16:13 ` James Morse
2020-05-12 16:53 ` Alexandru Elisei
2020-05-27 8:41 ` Marc Zyngier
2020-05-27 8:45 ` Alexandru Elisei
2020-04-22 12:00 ` [PATCH 04/26] arm64: Detect the ARMv8.4 TTL feature Marc Zyngier
2020-04-27 15:55 ` Suzuki K Poulose
2020-04-22 12:00 ` [PATCH 05/26] arm64: Document SW reserved PTE/PMD bits in Stage-2 descriptors Marc Zyngier
2020-05-05 15:59 ` Andrew Scull
2020-05-06 9:39 ` Marc Zyngier
2020-05-06 10:11 ` Andrew Scull
2020-04-22 12:00 ` [PATCH 06/26] arm64: Add level-hinted TLB invalidation helper Marc Zyngier
2020-05-05 17:16 ` Andrew Scull
2020-05-06 8:05 ` Marc Zyngier
2020-04-22 12:00 ` [PATCH 07/26] KVM: arm64: Add a level hint to __kvm_tlb_flush_vmid_ipa Marc Zyngier
2020-05-07 15:08 ` Andrew Scull
2020-05-07 15:13 ` Marc Zyngier
2020-04-22 12:00 ` [PATCH 08/26] KVM: arm64: Use TTL hint in when invalidating stage-2 translations Marc Zyngier
2020-05-07 15:13 ` Andrew Scull
2020-05-12 12:04 ` James Morse
2020-05-13 9:06 ` Andrew Scull
2020-05-27 8:59 ` Marc Zyngier
2020-05-12 17:26 ` James Morse
2020-04-22 12:00 ` [PATCH 09/26] KVM: arm64: vgic-v3: Take cpu_if pointer directly instead of vcpu Marc Zyngier
2020-05-07 16:26 ` James Morse
2020-05-08 12:20 ` Marc Zyngier
2020-04-22 12:00 ` [PATCH 10/26] KVM: arm64: Refactor vcpu_{read,write}_sys_reg Marc Zyngier
2020-05-26 16:28 ` James Morse
2020-05-27 10:04 ` Marc Zyngier
2020-04-22 12:00 ` [PATCH 11/26] KVM: arm64: Add missing reset handlers for PMU emulation Marc Zyngier
2020-05-26 16:29 ` James Morse
2020-04-22 12:00 ` [PATCH 12/26] KVM: arm64: Move sysreg reset check to boot time Marc Zyngier
2020-04-22 12:00 ` [PATCH 13/26] KVM: arm64: Introduce accessor for ctxt->sys_reg Marc Zyngier
2020-04-22 12:00 ` [PATCH 14/26] KVM: arm64: hyp: Use ctxt_sys_reg/__vcpu_sys_reg instead of raw sys_regs access Marc Zyngier
2020-04-22 12:00 ` [PATCH 15/26] KVM: arm64: sve: Use __vcpu_sys_reg() " Marc Zyngier
2020-04-22 12:00 ` [PATCH 16/26] KVM: arm64: pauth: Use ctxt_sys_reg() " Marc Zyngier
2020-04-22 12:00 ` [PATCH 17/26] KVM: arm64: debug: " Marc Zyngier
2020-04-22 12:00 ` [PATCH 18/26] KVM: arm64: Don't use empty structures as CPU reset state Marc Zyngier
2020-04-24 4:07 ` Zenghui Yu
2020-04-24 7:45 ` Marc Zyngier
2020-04-28 1:34 ` Zengtao (B)
2020-04-22 12:00 ` [PATCH 19/26] KVM: arm64: Make struct kvm_regs userspace-only Marc Zyngier
2020-05-26 16:29 ` James Morse
2020-05-27 10:22 ` Marc Zyngier
2020-04-22 12:00 ` [PATCH 20/26] KVM: arm64: Move ELR_EL1 to the system register array Marc Zyngier
2020-05-26 16:29 ` James Morse
2020-05-27 10:36 ` Marc Zyngier
2020-04-22 12:00 ` [PATCH 21/26] KVM: arm64: Move SP_EL1 " Marc Zyngier
2020-05-26 16:29 ` James Morse
2020-04-22 12:00 ` [PATCH 22/26] KVM: arm64: Disintegrate SPSR array Marc Zyngier
2020-05-26 16:30 ` James Morse
2020-04-22 12:00 ` [PATCH 23/26] KVM: arm64: Move SPSR_EL1 to the system register array Marc Zyngier
2020-05-26 16:30 ` James Morse
2020-04-22 12:00 ` [PATCH 24/26] KVM: arm64: timers: Rename kvm_timer_sync_hwstate to kvm_timer_sync_user Marc Zyngier
2020-04-22 12:00 ` [PATCH 25/26] KVM: arm64: timers: Move timer registers to the sys_regs file Marc Zyngier
2020-04-22 12:00 ` [PATCH 26/26] KVM: arm64: Parametrize exception entry with a target EL Marc Zyngier
2020-05-19 10:44 ` Mark Rutland
2020-05-27 9:34 ` Marc Zyngier
2020-05-27 14:41 ` Mark Rutland
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