From: Quentin Perret <qperret@google.com>
To: Yanan Wang <wangyanan55@huawei.com>
Cc: Marc Zyngier <maz@kernel.org>, Will Deacon <will@kernel.org>,
Alexandru Elisei <alexandru.elisei@arm.com>,
kvmarm@lists.cs.columbia.edu,
linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org,
Catalin Marinas <catalin.marinas@arm.com>,
James Morse <james.morse@arm.com>,
Julien Thierry <julien.thierry.kdev@gmail.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Gavin Shan <gshan@redhat.com>,
wanghaibin.wang@huawei.com, zhukeqian1@huawei.com,
yuzenghui@huawei.com
Subject: Re: [PATCH v5 6/6] KVM: arm64: Distinguish cases of memcache allocations completely
Date: Wed, 2 Jun 2021 11:07:53 +0000 [thread overview]
Message-ID: <YLdmiTfgz1EqBsJd@google.com> (raw)
In-Reply-To: <20210415115032.35760-7-wangyanan55@huawei.com>
On Thursday 15 Apr 2021 at 19:50:32 (+0800), Yanan Wang wrote:
> With a guest translation fault, the memcache pages are not needed if KVM
> is only about to install a new leaf entry into the existing page table.
> And with a guest permission fault, the memcache pages are also not needed
> for a write_fault in dirty-logging time if KVM is only about to update
> the existing leaf entry instead of collapsing a block entry into a table.
>
> By comparing fault_granule and vma_pagesize, cases that require allocations
> from memcache and cases that don't can be distinguished completely.
>
> Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
> ---
> arch/arm64/kvm/mmu.c | 25 ++++++++++++-------------
> 1 file changed, 12 insertions(+), 13 deletions(-)
>
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index aa536392b308..9e35aa5d29f2 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -895,19 +895,6 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> gfn = fault_ipa >> PAGE_SHIFT;
> mmap_read_unlock(current->mm);
>
> - /*
> - * Permission faults just need to update the existing leaf entry,
> - * and so normally don't require allocations from the memcache. The
> - * only exception to this is when dirty logging is enabled at runtime
> - * and a write fault needs to collapse a block entry into a table.
> - */
> - if (fault_status != FSC_PERM || (logging_active && write_fault)) {
> - ret = kvm_mmu_topup_memory_cache(memcache,
> - kvm_mmu_cache_min_pages(kvm));
> - if (ret)
> - return ret;
> - }
> -
> mmu_seq = vcpu->kvm->mmu_notifier_seq;
> /*
> * Ensure the read of mmu_notifier_seq happens before we call
> @@ -970,6 +957,18 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> else if (cpus_have_const_cap(ARM64_HAS_CACHE_DIC))
> prot |= KVM_PGTABLE_PROT_X;
>
> + /*
> + * Allocations from the memcache are required only when granule of the
> + * lookup level where the guest fault happened exceeds vma_pagesize,
> + * which means new page tables will be created in the fault handlers.
> + */
> + if (fault_granule > vma_pagesize) {
> + ret = kvm_mmu_topup_memory_cache(memcache,
> + kvm_mmu_cache_min_pages(kvm));
> + if (ret)
> + return ret;
> + }
You're now doing the top-up in the kvm->mmu_lock critical section. Isn't
this more or less what we try to avoid by using a memory cache?
Thanks,
Quentin
next prev parent reply other threads:[~2021-06-02 11:08 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-15 11:50 [PATCH v5 0/6] KVM: arm64: Improve efficiency of stage2 page table Yanan Wang
2021-04-15 11:50 ` [PATCH v5 1/6] KVM: arm64: Introduce KVM_PGTABLE_S2_GUEST stage-2 flag Yanan Wang
2021-06-02 10:43 ` Quentin Perret
2021-06-03 12:36 ` wangyanan (Y)
2021-04-15 11:50 ` [PATCH v5 2/6] KVM: arm64: Move D-cache flush to the fault handlers Yanan Wang
[not found] ` <877djc1sca.wl-maz@kernel.org>
2021-06-02 10:49 ` Quentin Perret
2021-06-03 12:33 ` wangyanan (Y)
2021-04-15 11:50 ` [PATCH v5 3/6] KVM: arm64: Add mm_ops member for structure stage2_attr_data Yanan Wang
2021-04-15 11:50 ` [PATCH v5 4/6] KVM: arm64: Provide invalidate_icache_range at non-VHE EL2 Yanan Wang
[not found] ` <875yyw1s73.wl-maz@kernel.org>
2021-06-03 12:34 ` wangyanan (Y)
2021-04-15 11:50 ` [PATCH v5 5/6] KVM: arm64: Move I-cache flush to the fault handlers Yanan Wang
2021-06-02 10:58 ` Quentin Perret
2021-06-03 12:35 ` wangyanan (Y)
2021-04-15 11:50 ` [PATCH v5 6/6] KVM: arm64: Distinguish cases of memcache allocations completely Yanan Wang
2021-06-02 11:07 ` Quentin Perret [this message]
2021-06-03 12:52 ` wangyanan (Y)
2021-05-12 12:54 ` [PATCH v5 0/6] KVM: arm64: Improve efficiency of stage2 page table wangyanan (Y)
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YLdmiTfgz1EqBsJd@google.com \
--to=qperret@google.com \
--cc=alexandru.elisei@arm.com \
--cc=catalin.marinas@arm.com \
--cc=gshan@redhat.com \
--cc=james.morse@arm.com \
--cc=julien.thierry.kdev@gmail.com \
--cc=kvm@vger.kernel.org \
--cc=kvmarm@lists.cs.columbia.edu \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=maz@kernel.org \
--cc=suzuki.poulose@arm.com \
--cc=wanghaibin.wang@huawei.com \
--cc=wangyanan55@huawei.com \
--cc=will@kernel.org \
--cc=yuzenghui@huawei.com \
--cc=zhukeqian1@huawei.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).