linux-kernel - Re: [PATCH v3 0/3] SVM 5-level page table support

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Date:   Mon, 23 Aug 2021 10:15:49 -0500
From:   Wei Huang <wei.huang2@....com>
To:     Maxim Levitsky <mlevitsk@...hat.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, vkuznets@...hat.com,
        seanjc@...gle.com, wanpengli@...cent.com, jmattson@...gle.com,
        joro@...tes.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, x86@...nel.org, hpa@...or.com
Subject: Re: [PATCH v3 0/3] SVM 5-level page table support

On 08/23 12:20, Maxim Levitsky wrote:
> On Thu, 2021-08-19 at 18:43 +0200, Paolo Bonzini wrote:
> > On 18/08/21 18:55, Wei Huang wrote:
> > > This patch set adds 5-level page table support for AMD SVM. When the
> > > 5-level page table is enabled on host OS, the nested page table for guest
> > > VMs will use the same format as host OS (i.e. 5-level NPT). These patches
> > > were tested with various combination of different settings and test cases
> > > (nested/regular VMs, AMD64/i686 kernels, kvm-unit-tests, etc.)
> > > 
> > > v2->v3:
> > >   * Change the way of building root_hpa by following the existing flow (Sean)
> > > 
> > > v1->v2:
> > >   * Remove v1's arch-specific get_tdp_level() and add a new parameter,
> > >     tdp_forced_root_level, to allow forced TDP level (Sean)
> > >   * Add additional comment on tdp_root table chaining trick and change the
> > >     PML root table allocation code (Sean)
> > >   * Revise Patch 1's commit msg (Sean and Jim)
> > > 
> > > Thanks,
> > > -Wei
> > > 
> > > Wei Huang (3):
> > >    KVM: x86: Allow CPU to force vendor-specific TDP level
> > >    KVM: x86: Handle the case of 5-level shadow page table
> > >    KVM: SVM: Add 5-level page table support for SVM
> > > 
> > >   arch/x86/include/asm/kvm_host.h |  6 ++--
> > >   arch/x86/kvm/mmu/mmu.c          | 56 ++++++++++++++++++++++-----------
> > >   arch/x86/kvm/svm/svm.c          | 13 ++++----
> > >   arch/x86/kvm/vmx/vmx.c          |  3 +-
> > >   4 files changed, 49 insertions(+), 29 deletions(-)
> > > 
> > 
> > Queued, thanks, with NULL initializations according to Tom's review.
> > 
> > Paolo
> > 
> 
> Hi,
> Yesterday while testing my SMM patches, I noticed a minor issue: 
> It seems that this patchset breaks my 32 bit nested VM testcase with NPT=0.
>

Could you elaborate the detailed setup? NPT=0 for KVM running on L1?
Which VM is 32bit - L1 or L2?

Thanks,
-Wei

> This hack makes it work again for me (I don't yet use TDP mmu).
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index caa3f9aee7d1..c25e0d40a620 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -3562,7 +3562,7 @@ static int mmu_alloc_special_roots(struct kvm_vcpu *vcpu)
>             mmu->shadow_root_level < PT64_ROOT_4LEVEL)
>                 return 0;
>  
> -       if (mmu->pae_root && mmu->pml4_root && mmu->pml5_root)
> +       if (mmu->pae_root && mmu->pml4_root)
>                 return 0;
>  
>         /*
> 
> 
> 
> Best regards,
> 	Maxim Levitsky
>