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

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Message-ID: <c10faf24c11fc86074945ca535572a8c5926dcf9.camel@redhat.com>
Date:   Mon, 23 Aug 2021 12:20:27 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Wei Huang <wei.huang2@....com>, kvm@...r.kernel.org
Cc:     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 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.

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