From: Yu Zhang <yu.c.zhang@linux.intel.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>,
Wei Huang <wei.huang2@amd.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
vkuznets@redhat.com, wanpengli@tencent.com, jmattson@google.com,
joro@8bytes.org, tglx@linutronix.de, mingo@redhat.com,
bp@alien8.de, x86@kernel.org, hpa@zytor.com
Subject: Re: [PATCH v2 1/3] KVM: x86: Allow CPU to force vendor-specific TDP level
Date: Tue, 10 Aug 2021 19:00:31 +0800 [thread overview]
Message-ID: <20210810110031.h7vaqf3nljwm3wym@linux.intel.com> (raw)
In-Reply-To: <0ac41a07-beeb-161e-9e5d-e45477106c01@redhat.com>
On Tue, Aug 10, 2021 at 11:25:27AM +0200, Paolo Bonzini wrote:
> On 10/08/21 09:40, Yu Zhang wrote:
> > About "host can't easily mirror L1's desired paging mode", could you please elaborate?
> > Thanks!
>
> Shadow pgae tables in KVM will always have 3 levels on 32-bit machines and
> 4/5 levels on 64-bit machines. L1 instead might have any number of levels
> from 2 to 5 (though of course not more than the host has).
Thanks Paolo.
I guess it's because, unlike EPT which are with either 4 or 5 levels, NPT's
level can range from 2 to 5, depending on the host paging mode...
>
> Therefore, when shadowing 32-bit NPT page tables, KVM has to add extra fixed
> levels on top of those that it's shadowing. See mmu_alloc_direct_roots for
> the code.
So when shadowing NPTs(can be 2/3 levels, depending on the paging mode in L1),
and if L0 Linux is running in 4/5 level mode, extra levels of paging structures
is needed in the shadow NPT.
But shadow EPT does not have such annoyance. Is above understanding correct?
B.R.
Yu
next prev parent reply other threads:[~2021-08-10 11:00 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-08 19:26 [PATCH v2 0/3] SVM 5-level page table support Wei Huang
2021-08-08 19:26 ` [PATCH v2 1/3] KVM: x86: Allow CPU to force vendor-specific TDP level Wei Huang
2021-08-09 3:58 ` Yu Zhang
2021-08-09 4:11 ` Wei Huang
2021-08-09 4:27 ` Yu Zhang
2021-08-09 4:33 ` Wei Huang
2021-08-09 6:42 ` Yu Zhang
2021-08-09 15:30 ` Sean Christopherson
2021-08-09 21:49 ` Jim Mattson
2021-08-10 9:23 ` Paolo Bonzini
2021-08-10 7:40 ` Yu Zhang
2021-08-10 9:25 ` Paolo Bonzini
2021-08-10 11:00 ` Yu Zhang [this message]
2021-08-10 12:47 ` Paolo Bonzini
2021-08-10 14:37 ` Yu Zhang
2021-08-08 19:26 ` [PATCH v2 2/3] KVM: x86: Handle the case of 5-level shadow page table Wei Huang
2021-08-09 15:17 ` Sean Christopherson
2021-08-09 17:03 ` Wei Huang
2021-08-08 19:26 ` [PATCH v2 3/3] KVM: SVM: Add 5-level page table support for SVM Wei Huang
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