From: Marc Zyngier <maz@kernel.org>
To: Will Deacon <will@kernel.org>
Cc: kvm@vger.kernel.org, kernel-team@android.com,
Srivatsa Vaddagiri <vatsa@codeaurora.org>,
linux-kernel@vger.kernel.org,
Shanker R Donthineni <sdonthineni@nvidia.com>,
kvmarm@lists.cs.columbia.edu,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 01/16] KVM: arm64: Generalise VM features into a set of flags
Date: Wed, 28 Jul 2021 10:41:00 +0100 [thread overview]
Message-ID: <875ywuepxv.wl-maz@kernel.org> (raw)
In-Reply-To: <20210727181026.GA19173@willie-the-truck>
On Tue, 27 Jul 2021 19:10:27 +0100,
Will Deacon <will@kernel.org> wrote:
>
> On Thu, Jul 15, 2021 at 05:31:44PM +0100, Marc Zyngier wrote:
> > We currently deal with a set of booleans for VM features,
> > while they could be better represented as set of flags
> > contained in an unsigned long, similarily to what we are
> > doing on the CPU side.
> >
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > ---
> > arch/arm64/include/asm/kvm_host.h | 12 +++++++-----
> > arch/arm64/kvm/arm.c | 5 +++--
> > arch/arm64/kvm/mmio.c | 3 ++-
> > 3 files changed, 12 insertions(+), 8 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> > index 41911585ae0c..4add6c27251f 100644
> > --- a/arch/arm64/include/asm/kvm_host.h
> > +++ b/arch/arm64/include/asm/kvm_host.h
> > @@ -122,7 +122,10 @@ struct kvm_arch {
> > * should) opt in to this feature if KVM_CAP_ARM_NISV_TO_USER is
> > * supported.
> > */
> > - bool return_nisv_io_abort_to_user;
> > +#define KVM_ARCH_FLAG_RETURN_NISV_IO_ABORT_TO_USER 0
> > + /* Memory Tagging Extension enabled for the guest */
> > +#define KVM_ARCH_FLAG_MTE_ENABLED 1
> > + unsigned long flags;
>
> One downside of packing all these together is that updating 'flags' now
> requires an atomic rmw sequence (i.e. set_bit()). Then again, that's
> probably for the best anyway given that kvm_vm_ioctl_enable_cap() looks
> like it doesn't hold any locks.
That, and these operations are supposed to be extremely rare anyway.
>
> > /*
> > * VM-wide PMU filter, implemented as a bitmap and big enough for
> > @@ -133,9 +136,6 @@ struct kvm_arch {
> >
> > u8 pfr0_csv2;
> > u8 pfr0_csv3;
> > -
> > - /* Memory Tagging Extension enabled for the guest */
> > - bool mte_enabled;
> > };
> >
> > struct kvm_vcpu_fault_info {
> > @@ -777,7 +777,9 @@ bool kvm_arm_vcpu_is_finalized(struct kvm_vcpu *vcpu);
> > #define kvm_arm_vcpu_sve_finalized(vcpu) \
> > ((vcpu)->arch.flags & KVM_ARM64_VCPU_SVE_FINALIZED)
> >
> > -#define kvm_has_mte(kvm) (system_supports_mte() && (kvm)->arch.mte_enabled)
> > +#define kvm_has_mte(kvm) \
> > + (system_supports_mte() && \
> > + test_bit(KVM_ARCH_FLAG_MTE_ENABLED, &(kvm)->arch.flags))
>
> Not an issue with this patch, but I just noticed that the
> system_supports_mte() check is redundant here as we only allow the flag to
> be set if that's already the case.
It allows us to save a memory access if system_supports_mte() is false
(it is eventually implemented as a static key). On the other hand,
there is so much inlining due to it being a non-final cap that we
probably lose on that too...
M.
--
Without deviation from the norm, progress is not possible.
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next prev parent reply other threads:[~2021-07-28 9:41 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-15 16:31 [PATCH 00/16] KVM: arm64: MMIO guard PV services Marc Zyngier
2021-07-15 16:31 ` [PATCH 01/16] KVM: arm64: Generalise VM features into a set of flags Marc Zyngier
2021-07-27 18:10 ` Will Deacon
2021-07-28 9:41 ` Marc Zyngier [this message]
2021-07-28 14:51 ` Steven Price
2021-07-15 16:31 ` [PATCH 02/16] KVM: arm64: Don't issue CMOs when the physical address is invalid Marc Zyngier
2021-07-19 17:18 ` Quentin Perret
2021-07-20 8:04 ` Marc Zyngier
2021-07-27 18:10 ` Will Deacon
2021-07-28 9:45 ` Marc Zyngier
2021-07-15 16:31 ` [PATCH 03/16] KVM: arm64: Turn kvm_pgtable_stage2_set_owner into kvm_pgtable_stage2_annotate Marc Zyngier
2021-07-20 10:09 ` Quentin Perret
2021-07-20 10:21 ` Marc Zyngier
2021-07-20 10:38 ` Quentin Perret
2021-07-20 11:20 ` Marc Zyngier
2021-07-20 11:36 ` Quentin Perret
2021-07-20 13:13 ` Marc Zyngier
2021-07-15 16:31 ` [PATCH 04/16] KVM: arm64: Add MMIO checking infrastructure Marc Zyngier
2021-07-20 11:13 ` Quentin Perret
2021-07-20 13:15 ` Marc Zyngier
2021-07-20 15:49 ` Quentin Perret
2021-07-22 18:04 ` Marc Zyngier
2021-07-23 10:16 ` Quentin Perret
2021-07-27 18:11 ` Will Deacon
2021-07-28 9:57 ` Marc Zyngier
2021-07-30 12:26 ` Will Deacon
2021-07-30 13:04 ` Marc Zyngier
2021-07-30 12:58 ` Quentin Perret
2021-07-15 16:31 ` [PATCH 05/16] KVM: arm64: Plumb MMIO checking into the fault handling Marc Zyngier
2021-07-27 18:11 ` Will Deacon
2021-07-28 10:21 ` Marc Zyngier
2021-07-30 12:38 ` Will Deacon
2021-07-15 16:31 ` [PATCH 06/16] KVM: arm64: Force a full unmap on vpcu reinit Marc Zyngier
2021-07-27 18:11 ` Will Deacon
2021-07-28 10:38 ` Marc Zyngier
2021-07-30 12:50 ` Will Deacon
2021-07-15 16:31 ` [PATCH 07/16] KVM: arm64: Wire MMIO guard hypercalls Marc Zyngier
2021-07-27 18:11 ` Will Deacon
2021-07-28 10:47 ` Marc Zyngier
2021-07-30 13:11 ` Will Deacon
2021-08-01 11:20 ` Marc Zyngier
2021-07-15 16:31 ` [PATCH 08/16] KVM: arm64: Add tracepoint for failed MMIO guard check Marc Zyngier
2021-07-15 16:31 ` [PATCH 09/16] KVM: arm64: Advertise a capability for MMIO guard Marc Zyngier
2021-07-15 16:31 ` [PATCH 10/16] KVM: arm64: Add some documentation for the MMIO guard feature Marc Zyngier
2021-07-21 21:17 ` Andrew Jones
2021-07-23 13:30 ` Marc Zyngier
2021-07-23 13:38 ` Andrew Jones
2021-07-23 13:52 ` Marc Zyngier
2021-07-15 16:31 ` [PATCH 11/16] firmware/smccc: Call arch-specific hook on discovering KVM services Marc Zyngier
2021-07-15 16:31 ` [PATCH 12/16] mm/ioremap: Add arch-specific callbacks on ioremap/iounmap calls Marc Zyngier
2021-07-27 18:12 ` Will Deacon
2021-07-28 11:01 ` Marc Zyngier
2021-07-30 14:07 ` Will Deacon
2021-07-15 16:31 ` [PATCH 13/16] arm64: Implement ioremap/iounmap hooks calling into KVM's MMIO guard Marc Zyngier
2021-07-15 16:31 ` [PATCH 14/16] arm64: Enroll into KVM's MMIO guard if required Marc Zyngier
2021-07-15 16:31 ` [PATCH 15/16] arm64: Add a helper to retrieve the PTE of a fixmap Marc Zyngier
2021-07-20 11:16 ` Quentin Perret
2021-07-15 16:31 ` [PATCH 16/16] arm64: Register earlycon fixmap with the MMIO guard Marc Zyngier
2021-07-21 21:42 ` [PATCH 00/16] KVM: arm64: MMIO guard PV services Andrew Jones
2021-07-22 10:00 ` Marc Zyngier
2021-07-22 13:25 ` Andrew Jones
2021-07-22 15:30 ` Marc Zyngier
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