From: Steven Price <steven.price@arm.com>
To: Marc Zyngier <maz@kernel.org>, Will Deacon <will@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org,
kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org, qperret@google.com,
dbrazdil@google.com, Srivatsa Vaddagiri <vatsa@codeaurora.org>,
Shanker R Donthineni <sdonthineni@nvidia.com>,
James Morse <james.morse@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Alexandru Elisei <alexandru.elisei@arm.com>,
kernel-team@android.com
Subject: Re: [PATCH 01/16] KVM: arm64: Generalise VM features into a set of flags
Date: Wed, 28 Jul 2021 15:51:00 +0100 [thread overview]
Message-ID: <716fffdb-580a-bc70-478a-a54912a77c82@arm.com> (raw)
In-Reply-To: <875ywuepxv.wl-maz@kernel.org>
On 28/07/2021 10:41, Marc Zyngier wrote:
> 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...
My original logic was that system_supports_mte() checks
IS_ENABLED(CONFIG_ARM64_MTE) - so this enables the code guarded with
kvm_has_mte() to be compiled out if CONFIG_ARM64_MTE is disabled.
Indeed it turns at we currently rely on this (with CONFIG_ARM64_MTE
disabled):
aarch64-linux-gnu-ld: arch/arm64/kvm/mmu.o: in function `sanitise_mte_tags':
/home/stepri01/work/linux/arch/arm64/kvm/mmu.c:887: undefined reference to `mte_clear_page_tags'
aarch64-linux-gnu-ld: arch/arm64/kvm/guest.o: in function `kvm_vm_ioctl_mte_copy_tags':
/home/stepri01/work/linux/arch/arm64/kvm/guest.c:1066: undefined reference to `mte_copy_tags_to_user'
aarch64-linux-gnu-ld: /home/stepri01/work/linux/arch/arm64/kvm/guest.c:1074: undefined reference to `mte_copy_tags_from_user'
Obviously we could pull just the IS_ENABLED() into kvm_has_mte() instead.
Steve
next prev parent reply other threads:[~2021-07-28 14:51 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
2021-07-28 14:51 ` Steven Price [this message]
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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