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From: James Morse <james.morse@arm.com>
To: Marc Zyngier <maz@kernel.org>
Cc: "Julien Thierry" <julien.thierry.kdev@gmail.com>,
	"Suzuki K Poulose" <suzuki.poulose@arm.com>,
	"James Hogan" <jhogan@kernel.org>,
	"Paul Mackerras" <paulus@ozlabs.org>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	"Sean Christopherson" <sean.j.christopherson@intel.com>,
	"Vitaly Kuznetsov" <vkuznets@redhat.com>,
	"Wanpeng Li" <wanpengli@tencent.com>,
	"Jim Mattson" <jmattson@google.com>,
	"Joerg Roedel" <joro@8bytes.org>,
	linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, linux-mips@vger.kernel.org,
	kvm-ppc@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH 7/7] KVM: arm/arm64: Elide CMOs when unmapping a range
Date: Wed, 18 Dec 2019 15:07:48 +0000	[thread overview]
Message-ID: <0c832b27-7041-a6c8-31c0-d71a25c6f5b8@arm.com> (raw)
In-Reply-To: <20191213182503.14460-8-maz@kernel.org>

Hi Marc,

On 13/12/2019 18:25, Marc Zyngier wrote:
> If userspace issues a munmap() on a set of pages, there is no
> expectation that the pages are cleaned to the PoC.

(Pedantry: Clean and invalidate. If the guest wrote through a device mapping, we ditch any
clean+stale lines with this path, meaning swapout saves the correct values)


> So let's
> not do more work than strictly necessary, and set the magic
> flag that avoids CMOs in this case.

I think this assumes the pages went from anonymous->free, so no-one cares about the contents.

If the pages are backed by a file, won't dirty pages will still get written back before
the page is free? (e.g. EFI flash 'file' mmap()ed in)

What if this isn't the only mapping of the page? Can't it be swapped out from another VMA?
(tenuous example, poor man's memory mirroring?)


Thanks,

James

  reply	other threads:[~2019-12-18 15:07 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-13 18:24 [PATCH 0/7] KVM: arm/arm64: Help VMs dying quicker Marc Zyngier
2019-12-13 18:24 ` [PATCH 1/7] KVM: Pass mmu_notifier_range down to kvm_unmap_hva_range() Marc Zyngier
2019-12-13 18:59   ` Suzuki Kuruppassery Poulose
2019-12-14 10:37     ` Marc Zyngier
2019-12-15 10:27   ` Marc Zyngier
2020-01-15 18:10   ` Paolo Bonzini
2019-12-13 18:24 ` [PATCH 2/7] KVM: arm/arm64: Pass flags along Stage-2 unmapping functions Marc Zyngier
2019-12-13 18:24 ` [PATCH 3/7] KVM: arm/arm64: Condition cache maintenance on unmap with a flag Marc Zyngier
2019-12-13 18:25 ` [PATCH 4/7] KVM: arm/arm64: Condition TLB " Marc Zyngier
2019-12-13 18:25 ` [PATCH 5/7] KVM: arm/arm64: Elide both CMOs and TBLIs on freeing the whole Stage-2 Marc Zyngier
2019-12-13 18:25 ` [PATCH 6/7] KVM: arm/arm64: Elide CMOs when retrying a block mapping Marc Zyngier
2019-12-13 18:25 ` [PATCH 7/7] KVM: arm/arm64: Elide CMOs when unmapping a range Marc Zyngier
2019-12-18 15:07   ` James Morse [this message]
2019-12-18 15:30     ` Marc Zyngier
2019-12-19 13:46       ` James Morse

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