From: Paolo Bonzini <pbonzini@redhat.com>
To: Sean Christopherson <seanjc@google.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
Lai Jiangshan <jiangshan.ljs@antgroup.com>,
Jonathan Corbet <corbet@lwn.net>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
linux-doc@vger.kernel.org
Subject: Re: [RFC PATCH V3 2/4] KVM: X86: Introduce role.glevel for level expanded pagetable
Date: Wed, 13 Apr 2022 16:46:00 +0200 [thread overview]
Message-ID: <d2122fb0-7327-0490-9077-c69bbfba4830@redhat.com> (raw)
In-Reply-To: <YlbhVov4cvM26FnC@google.com>
On 4/13/22 16:42, Sean Christopherson wrote:
> On Wed, Apr 13, 2022, Paolo Bonzini wrote:
>> On 4/12/22 23:31, Sean Christopherson wrote:
>>> We don't need 4 bits for this. Crossing our fingers that we never had to shadow
>>> a 2-level guest with a 6-level host, we can do:
>>>
>>> unsigned passthrough_delta:2;
>>>
>> Basically, your passthrough_delta is level - glevel in Jiangshan's patches.
>> You'll need 3 bits anyway when we remove direct later (that would be
>> passthrough_delta == level).
>
> Are we planning on removing direct?
I think so, it's redundant and the code almost always checks
direct||passthrough (which would be passthrough_delta > 0 with your scheme).
>> Regarding the naming:
>>
>> * If we keep Jiangshan's logic, I don't like the glevel name very much, any
>> of mapping_level, target_level or direct_level would be clearer?
>
> I don't love any of these names, especially glevel, because the field doesn't
> strictly track the guest/mapping/target/direct level. That could obviously be
> remedied by making it valid at all times, but then the role would truly need 3
> bits (on top of direct) to track 5-level guest paging.
Yes, it would need 3 bits but direct can be removed.
>> * If we go with yours, I would call the field "passthrough_levels".
>
> Hmm, it's not a raw level though.
Hence the plural. :)
Paolo
next prev parent reply other threads:[~2022-04-13 14:46 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-30 13:21 [RFC PATCH V3 0/4] KVM: X86: Add and use shadow page with level expanded or acting as pae_root Lai Jiangshan
2022-03-30 13:21 ` [RFC PATCH V3 1/4] KVM: X86: Add arguement gfn and role to kvm_mmu_alloc_page() Lai Jiangshan
2022-03-30 13:21 ` [RFC PATCH V3 2/4] KVM: X86: Introduce role.glevel for level expanded pagetable Lai Jiangshan
2022-03-30 16:01 ` Lai Jiangshan
2022-04-12 21:31 ` Sean Christopherson
2022-04-13 4:13 ` Lai Jiangshan
2022-04-13 8:38 ` Paolo Bonzini
2022-04-13 14:42 ` Sean Christopherson
2022-04-13 14:46 ` Paolo Bonzini [this message]
2022-04-13 15:32 ` Sean Christopherson
2022-04-13 16:03 ` Paolo Bonzini
2022-04-14 15:51 ` Sean Christopherson
2022-04-14 16:32 ` Lai Jiangshan
2022-03-30 13:21 ` [RFC PATCH V3 3/4] KVM: X86: Alloc role.pae_root shadow page Lai Jiangshan
2022-04-12 21:14 ` Sean Christopherson
2022-04-14 9:07 ` Lai Jiangshan
2022-04-14 9:08 ` Paolo Bonzini
2022-04-14 9:32 ` Lai Jiangshan
2022-04-14 10:04 ` Paolo Bonzini
2022-04-14 11:06 ` Lai Jiangshan
2022-04-14 14:12 ` Paolo Bonzini
2022-04-14 14:42 ` Sean Christopherson
2022-04-14 13:35 ` Lai Jiangshan
2022-04-14 14:52 ` Sean Christopherson
2022-03-30 13:21 ` [RFC PATCH V3 4/4] KVM: X86: Use passthrough and pae_root shadow page for 32bit guests Lai Jiangshan
2022-04-12 21:34 ` Sean Christopherson
2022-04-12 9:35 ` [RFC PATCH V3 0/4] KVM: X86: Add and use shadow page with level expanded or acting as pae_root Lai Jiangshan
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