From: Sean Christopherson <seanjc@google.com>
To: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
Paolo Bonzini <pbonzini@redhat.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Maxim Levitsky <mlevitsk@redhat.com>,
David Matlack <dmatlack@google.com>,
Lai Jiangshan <jiangshan.ljs@antgroup.com>
Subject: Re: [PATCH V3 11/12] KVM: X86/MMU: Don't use mmu->pae_root when shadowing PAE NPT in 64-bit host
Date: Tue, 19 Jul 2022 23:26:07 +0000 [thread overview]
Message-ID: <Ytc9j/ayzTfm6Rti@google.com> (raw)
In-Reply-To: <20220521131700.3661-12-jiangshanlai@gmail.com>
On Sat, May 21, 2022, Lai Jiangshan wrote:
> From: Lai Jiangshan <jiangshan.ljs@antgroup.com>
>
> Allocate the tables when allocating the local shadow page.
This absolutely needs a much more verbose changelog.
> Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
> ---
> arch/x86/kvm/mmu/mmu.c | 17 +++++++++--------
> 1 file changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 63c2b2c6122c..73e6a8e1e1a9 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -1809,10 +1809,12 @@ static bool using_local_root_page(struct kvm_mmu *mmu)
> * 2 or 3 levels of local shadow pages on top of non-local shadow pages.
> *
> * Local shadow pages are locally allocated. If the local shadow page's level
> - * is PT32E_ROOT_LEVEL, it will use the preallocated mmu->pae_root for its
> - * sp->spt. Because sp->spt may need to be put in the 32 bits CR3 (even in
> - * x86_64) or decrypted. Using the preallocated one to handle these
> - * requirements makes the allocation simpler.
> + * is PT32E_ROOT_LEVEL, and it is not shadowing nested NPT for 32-bit L1 in
> + * 64-bit L0 (or said when the shadow pagetable's level is PT32E_ROOT_LEVEL),
> + * it will use the preallocated mmu->pae_root for its sp->spt. Because sp->spt
> + * need to be put in the 32-bit CR3 (even in 64-bit host) or decrypted. Using
> + * the preallocated one to handle these requirements makes the allocation
> + * simpler.
> *
> * Local shadow pages are only visible to local VCPU except through
> * sp->parent_ptes rmap from their children, so they are not in the
> @@ -1852,13 +1854,12 @@ kvm_mmu_alloc_local_shadow_page(struct kvm_vcpu *vcpu, union kvm_mmu_page_role r
> sp->gfn = 0;
> sp->role = role;
> /*
> - * Use the preallocated mmu->pae_root when the shadow page's
> - * level is PT32E_ROOT_LEVEL which may need to be put in the 32 bits
> + * Use the preallocated mmu->pae_root when the shadow pagetable's
> + * level is PT32E_ROOT_LEVEL which need to be put in the 32 bits
> * CR3 (even in x86_64) or decrypted. The preallocated one is prepared
> * for the requirements.
> */
> - if (role.level == PT32E_ROOT_LEVEL &&
> - !WARN_ON_ONCE(!vcpu->arch.mmu->pae_root))
Why remove this WARN_ON_ONCE()? And shouldn't this also interact with
KVM: X86/MMU: Allocate mmu->pae_root for PAE paging on-demand
Actually, I think the series is buggy. That patch, which precedes this one, does
if (vcpu->arch.mmu->root_role.level != PT32E_ROOT_LEVEL)
return 0;
i.e. does NOT allocate pae_root for a 64-bit host, which means that running KVM
against the on-demand patch would result in the WARN firing and bad things happening.
> + if (vcpu->arch.mmu->root_role.level == PT32E_ROOT_LEVEL)
> sp->spt = vcpu->arch.mmu->pae_root;
> else
> sp->spt = kvm_mmu_memory_cache_alloc(&vcpu->arch.mmu_shadow_page_cache);
> --
> 2.19.1.6.gb485710b
>
next prev parent reply other threads:[~2022-07-19 23:26 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-21 13:16 [PATCH V3 00/12] KVM: X86/MMU: Use one-off local shadow page for special roots Lai Jiangshan
2022-05-21 13:16 ` [PATCH V3 01/12] KVM: X86/MMU: Verify PDPTE for nested NPT in PAE paging mode when page fault Lai Jiangshan
2022-07-19 21:17 ` Sean Christopherson
2022-05-21 13:16 ` [PATCH V3 02/12] KVM: X86/MMU: Add using_local_root_page() Lai Jiangshan
2022-05-26 21:28 ` David Matlack
2022-05-26 21:38 ` Sean Christopherson
2022-07-19 22:03 ` Sean Christopherson
2022-05-21 13:16 ` [PATCH V3 03/12] KVM: X86/MMU: Reduce a check in using_local_root_page() for common cases Lai Jiangshan
2022-05-21 13:16 ` [PATCH V3 04/12] KVM: X86/MMU: Add local shadow pages Lai Jiangshan
2022-05-26 21:38 ` David Matlack
2022-05-26 22:01 ` David Matlack
2022-07-20 0:35 ` Sean Christopherson
2022-05-21 13:16 ` [PATCH V3 05/12] KVM: X86/MMU: Link PAE root pagetable with its children Lai Jiangshan
2022-07-19 22:21 ` Sean Christopherson
2022-05-21 13:16 ` [PATCH V3 06/12] KVM: X86/MMU: Activate local shadow pages and remove old logic Lai Jiangshan
2022-05-21 13:16 ` [PATCH V3 07/12] KVM: X86/MMU: Remove the check of the return value of to_shadow_page() Lai Jiangshan
2022-07-19 22:42 ` Sean Christopherson
2022-05-21 13:16 ` [PATCH V3 08/12] KVM: X86/MMU: Allocate mmu->pae_root for PAE paging on-demand Lai Jiangshan
2022-07-19 23:08 ` Sean Christopherson
2022-07-20 0:07 ` Sean Christopherson
2022-05-21 13:16 ` [PATCH V3 09/12] KVM: X86/MMU: Move the verifying of NPT's PDPTE in FNAME(fetch) Lai Jiangshan
2022-07-19 23:21 ` Sean Christopherson
2022-05-21 13:16 ` [PATCH V3 10/12] KVM: X86/MMU: Remove unused INVALID_PAE_ROOT and IS_VALID_PAE_ROOT Lai Jiangshan
2022-07-19 23:11 ` Sean Christopherson
2022-05-21 13:16 ` [PATCH V3 11/12] KVM: X86/MMU: Don't use mmu->pae_root when shadowing PAE NPT in 64-bit host Lai Jiangshan
2022-07-19 23:26 ` Sean Christopherson [this message]
2022-07-19 23:27 ` Sean Christopherson
2022-05-21 13:17 ` [PATCH V3 12/12] KVM: X86/MMU: Remove mmu_alloc_special_roots() Lai Jiangshan
2022-05-26 8:49 ` [PATCH V3 00/12] KVM: X86/MMU: Use one-off local shadow page for special roots Lai Jiangshan
2022-05-26 20:27 ` David Matlack
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