Re: [RFC PATCH 01/37] KVM: x86/mmu: Store the address space ID directly in kvm_mmu_page_role

From: Oliver Upton <oliver.upton@linux.dev>
To: "Yang, Weijiang" <weijiang.yang@intel.com>
Cc: David Matlack <dmatlack@google.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Marc Zyngier <maz@kernel.org>, James Morse <james.morse@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
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	Atish Patra <atishp@atishpatra.org>,
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	Sean" <seanjc@google.com>,
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	Anshuman Khandual <anshuman.khandual@arm.com>,
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Subject: Re: [RFC PATCH 01/37] KVM: x86/mmu: Store the address space ID directly in kvm_mmu_page_role
Date: Fri, 9 Dec 2022 17:24:50 +0000	[thread overview]
Message-ID: <Y5NvYmxpy6BPkmpW@google.com> (raw)
In-Reply-To: <22fe2332-497e-fe30-0155-e026b0eded97@intel.com>

On Fri, Dec 09, 2022 at 10:37:47AM +0800, Yang, Weijiang wrote:
> 
> On 12/9/2022 3:38 AM, David Matlack wrote:
> > Rename kvm_mmu_page_role.smm with kvm_mmu_page_role.as_id and use it
> > directly as the address space ID throughout the KVM MMU code. This
> > eliminates a needless level of indirection, kvm_mmu_role_as_id(), and
> > prepares for making kvm_mmu_page_role architecture-neutral.
> > 
> > Signed-off-by: David Matlack <dmatlack@google.com>
> > ---
> >   arch/x86/include/asm/kvm_host.h |  4 ++--
> >   arch/x86/kvm/mmu/mmu.c          |  6 +++---
> >   arch/x86/kvm/mmu/mmu_internal.h | 10 ----------
> >   arch/x86/kvm/mmu/tdp_iter.c     |  2 +-
> >   arch/x86/kvm/mmu/tdp_mmu.c      | 12 ++++++------
> >   5 files changed, 12 insertions(+), 22 deletions(-)
> > 
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index aa4eb8cfcd7e..0a819d40131a 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -348,7 +348,7 @@ union kvm_mmu_page_role {
> >   		 * simple shift.  While there is room, give it a whole
> >   		 * byte so it is also faster to load it from memory.
> >   		 */
> > -		unsigned smm:8;
> > +		unsigned as_id:8;
> >   	};
> >   };
> > @@ -2056,7 +2056,7 @@ enum {
> >   # define __KVM_VCPU_MULTIPLE_ADDRESS_SPACE
> >   # define KVM_ADDRESS_SPACE_NUM 2
> >   # define kvm_arch_vcpu_memslots_id(vcpu) ((vcpu)->arch.hflags & HF_SMM_MASK ? 1 : 0)
> > -# define kvm_memslots_for_spte_role(kvm, role) __kvm_memslots(kvm, (role).smm)
> > +# define kvm_memslots_for_spte_role(kvm, role) __kvm_memslots(kvm, (role).as_id)
> >   #else
> >   # define kvm_memslots_for_spte_role(kvm, role) __kvm_memslots(kvm, 0)
> >   #endif
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index 4d188f056933..f375b719f565 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -5056,7 +5056,7 @@ kvm_calc_cpu_role(struct kvm_vcpu *vcpu, const struct kvm_mmu_role_regs *regs)
> >   	union kvm_cpu_role role = {0};
> >   	role.base.access = ACC_ALL;
> > -	role.base.smm = is_smm(vcpu);
> > +	role.base.as_id = is_smm(vcpu);
> 
> I'm not familiar with other architectures, is there similar conception as
> x86 smm mode?

For KVM/arm64:

No, we don't do anything like SMM emulation on x86. Architecturally
speaking, though, we do have a higher level of privilege typically
used by firmware on arm64, called EL3.

I'll need to read David's series a bit more closely, but I'm inclined to
think that the page role is going to be rather arch-specific.

--
Thanks,
Oliver

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