On Mon, 2021-08-23 at 16:10 +0000, Sean Christopherson wrote:
> On Mon, Aug 23, 2021, Wei Huang wrote:
> > On 08/23 12:20, Maxim Levitsky wrote:
> > > 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)
>
> Maxim, I assume you hit this WARN and bail?
Yep.
>
> if (WARN_ON_ONCE(!tdp_enabled || mmu->pae_root || mmu->pml4_root ||
> mmu->pml5_root))
> return -EIO;
>
> Because as the comment states, KVM expects all the special roots to be allocated
> together. The 5-level paging supported breaks that assumption because pml5_root
> will be allocated iff the host is using 5-level paging.
>
> if (mmu->shadow_root_level > PT64_ROOT_4LEVEL) {
> pml5_root = (void *)get_zeroed_page(GFP_KERNEL_ACCOUNT);
> if (!pml5_root)
> goto err_pml5;
> }
>
> I think this is the least awful fix, I'll test and send a proper patch later today.
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 4853c033e6ce..93b2ed422b48 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -3548,6 +3548,7 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
> static int mmu_alloc_special_roots(struct kvm_vcpu *vcpu)
> {
> struct kvm_mmu *mmu = vcpu->arch.mmu;
> + bool need_pml5 = mmu->shadow_root_level > PT64_ROOT_4LEVEL;
> u64 *pml5_root = NULL;
> u64 *pml4_root = NULL;
> u64 *pae_root;
> @@ -3562,7 +3563,14 @@ 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)
> + /*
> + * NPT, the only paging mode that uses this horror, uses a fixed number
> + * of levels for the shadow page tables, e.g. all MMUs are 4-level or
> + * all MMus are 5-level. Thus, this can safely require that pml5_root
> + * is allocated if the other roots are valid and pml5 is needed, as any
> + * prior MMU would also have required pml5.
> + */
> + if (mmu->pae_root && mmu->pml4_root && (!need_pml5 || mmu->pml5_root))
> return 0;
>
> /*
> @@ -3570,7 +3578,7 @@ static int mmu_alloc_special_roots(struct kvm_vcpu *vcpu)
> * bail if KVM ends up in a state where only one of the roots is valid.
> */
> if (WARN_ON_ONCE(!tdp_enabled || mmu->pae_root || mmu->pml4_root ||
> - mmu->pml5_root))
> + (need_pml5 && mmu->pml5_root)))
> return -EIO;
>
> /*
>
> > > + if (mmu->pae_root && mmu->pml4_root)
> > > return 0;
> > >
> > > /*
Makes sense, works, and without digging too much into this
I expected this to be fixed by something like that, so:
Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
Thanks,
Best regards,
Maxim Levitsky
> > >
> > >
> > >
> > > Best regards,
> > > Maxim Levitsky
> > >
