linux-kernel - Re: [PATCH] svm/avic: iommu/amd: Flush IOMMU IRT after update all entries

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Date:   Mon, 25 Mar 2019 14:46:01 +0100
From:   "joro@...tes.org" <joro@...tes.org>
To:     "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>
Subject: Re: [PATCH] svm/avic: iommu/amd: Flush IOMMU IRT after update all
 entries

On Wed, Mar 20, 2019 at 08:14:56AM +0000, Suthikulpanit, Suravee wrote:
> When AVIC is enabled and the VM has discrete device assignment,
> the interrupt remapping table (IRT) is used to keep track of which
> destination APIC ID the IOMMU will inject the device interrput to.
> 
> This means every time a vcpu is blocked or context-switched (i.e.
> vcpu_blocking/unblocking() and vcpu_load/put()), the information
> in IRT must be updated and the IOMMU IRT flush command must be
> issued.
> 
> The current implementation flushes IOMMU IRT every time an entry
> is modified. If the assigned device has large number of interrupts
> (hence large number of entries), this would add large amount of
> overhead to vcpu context-switch. Instead, this can be optmized by
> only flush IRT once per vcpu context-switch per device after all
> IRT entries are modified.
> 
> The function amd_iommu_update_ga() is refactored to only update
> IRT entry, while the amd_iommu_sync_ga() is introduced to allow
> IRT flushing to be done separately.
> 
> Cc: Joerg Roedel <joro@...tes.org>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
> ---
>  arch/x86/kvm/svm.c        | 35 ++++++++++++++++++++++++++++++++++-
>  drivers/iommu/amd_iommu.c | 20 +++++++++++++++++---
>  include/linux/amd-iommu.h | 13 ++++++++++---
>  3 files changed, 61 insertions(+), 7 deletions(-)

For the IOMMU parts:

	Acked-by: Joerg Roedel <jroedel@...e.de>