Re: [PATCH RFC] KVM: x86: mmu: don't re-generate permissions/pkru_mask bitmasks when source is unchanged

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Subject: Re: [PATCH RFC] KVM: x86: mmu: don't re-generate permissions/pkru_mask bitmasks when source is unchanged
From: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
Date: Mon, 09 Jul 2018 18:33:27 +0200
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>, Radim Krčmář <rkrcmar@xxxxxxxxxx>, Jim Mattson <jmattson@xxxxxxxxxx>, Liran Alon <liran.alon@xxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx
In-reply-to: <20180709162357.15593-1-vkuznets@redhat.com> (Vitaly Kuznetsov's message of "Mon, 9 Jul 2018 18:23:57 +0200")
References: <20180709162357.15593-1-vkuznets@redhat.com>
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.3 (gnu/linux)

Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> writes:

> ...

I'm sorry for the screwed up Subject line)

-- 
  Vitaly

References:
- [PATCH RFC] KVM: x86: mmu: don't re-generate permissions/pkru_mask bitmasks when source is unchanged 1;5004;0c update_permission_bitmask()/update_pkru_bitmask() are rarely called under normal circumstances but nesting changes everything. E.g. for nVMX we call kvm_mmu_reset_context() from nested_vmx_load_cr3() which happens on nested vmexit/vmentry. init_kvm_mmu() in its turn call init_kvm_nested_mmu() or init_kvm_tdp_mmu() (which operate on arch.nested_mmu and arch.mmu respectively) which unconditionally do update_permission_bitmask()/ update_pkru_bitmask().
  - From: Vitaly Kuznetsov

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