| Date | Tue, 18 Apr 2023 15:29:46 +0100 | Subject | Re: [PATCH v3 55/60] arm64: kvm: avoid CONFIG_PGTABLE_LEVELS for runtime levels | From | Ryan Roberts <> |
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On 07/03/2023 14:05, Ard Biesheuvel wrote: > get_user_mapping_size() uses vabits_actual and CONFIG_PGTABLE_LEVELS to > provide the starting point for a table walk. This is fine for LVA, as > the number of translation levels is the same regardless of whether LVA > is enabled. However, with LPA2, this will no longer be the case, so > let's derive the number of levels from the number of VA bits directly. > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org> > --- > arch/arm64/kvm/mmu.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index d64be7b5f6692e8b..4e7c0f9a9c286c09 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -663,7 +663,7 @@ static int get_user_mapping_size(struct kvm *kvm, u64 addr) > .pgd = (kvm_pteref_t)kvm->mm->pgd, > .ia_bits = vabits_actual, > .start_level = (KVM_PGTABLE_MAX_LEVELS - > - CONFIG_PGTABLE_LEVELS), > + ARM64_HW_PGTABLE_LEVELS(pgt.ia_bits)), > .mm_ops = &kvm_user_mm_ops, > }; > kvm_pte_t pte = 0; /* Keep GCC quiet... */
You have the problem here that the KVM library (which isn't LPA2 aware) is walking a kernel page table, which may now be in LPA2 format. I think this works out ok as long as there are no physical addresses above 48 bits in the page table. But otherwise, I doubt it works out very well...
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