linux-kernel - Re: [PATCH v5.5 07/30] KVM: Let/force architectures to deal with arch specific memslot data

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Date:   Tue, 9 Nov 2021 01:39:53 +0100
From:   "Maciej S. Szmigiero" <maciej.szmigiero@...cle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Atish Patra <atish.patra@....com>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-mips@...r.kernel.org, kvm@...r.kernel.org,
        kvm-ppc@...r.kernel.org, kvm-riscv@...ts.infradead.org,
        Palmer Dabbelt <palmer@...belt.com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Ben Gardon <bgardon@...gle.com>, Marc Zyngier <maz@...nel.org>,
        Huacai Chen <chenhuacai@...nel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
        Paul Mackerras <paulus@...abs.org>,
        Anup Patel <anup.patel@....com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v5.5 07/30] KVM: Let/force architectures to deal with arch
 specific memslot data

On 04.11.2021 01:25, Sean Christopherson wrote:
> Pass the "old" slot to kvm_arch_prepare_memory_region() and force arch
> code to handle propagating arch specific data from "new" to "old" when
> necessary.  This is a baby step towards dynamically allocating "new" from
> the get go, and is a (very) minor performance boost on x86 due to not
> unnecessarily copying arch data.
> 
> For PPC HV, copy the rmap in the !CREATE and !DELETE paths, i.e. for MOVE
> and FLAGS_ONLY.  This is functionally a nop as the previous behavior
> would overwrite the pointer for CREATE, and eventually discard/ignore it
> for DELETE.
> 
> For x86, copy the arch data only for FLAGS_ONLY changes.  Unlike PPC HV,
> x86 needs to reallocate arch data in the MOVE case as the size of x86's
> allocations depend on the alignment of the memslot's gfn.
> 
> Opportunistically tweak kvm_arch_prepare_memory_region()'s param order to
> match the "commit" prototype.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>   arch/arm64/kvm/mmu.c               |  7 ++++---
>   arch/mips/kvm/mips.c               |  3 ++-
>   arch/powerpc/include/asm/kvm_ppc.h | 18 ++++++++++--------
>   arch/powerpc/kvm/book3s.c          | 12 ++++++------
>   arch/powerpc/kvm/book3s_hv.c       | 17 ++++++++++-------
>   arch/powerpc/kvm/book3s_pr.c       | 17 +++++++++--------
>   arch/powerpc/kvm/booke.c           |  5 +++--
>   arch/powerpc/kvm/powerpc.c         |  5 +++--
>   arch/s390/kvm/kvm-s390.c           |  3 ++-
>   arch/x86/kvm/x86.c                 | 15 +++++++++++----
>   include/linux/kvm_host.h           |  3 ++-
>   virt/kvm/kvm_main.c                |  5 +----
>   12 files changed, 63 insertions(+), 47 deletions(-)
> 

You didn't include the RISCV kvm_arch_prepare_memory_region() change here
(that's actually in patch 13 of this series) so bisection on that arch
will be broken between this patch and patch 13.

Thanks,
Maciej