Re: [RFC PATCH v11 01/29] KVM: Wrap kvm_gfn_range.pte in a per-action union
From: Sean Christopherson <seanjc@google.com>
Date: 2023-07-19 15:39:25
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kvm, kvm-riscv, kvmarm, linux-arm-kernel, linux-fsdevel, linux-mips, linux-mm, linux-riscv, linuxppc-dev, lkml
On Wed, Jul 19, 2023, Jarkko Sakkinen wrote:
On Wed Jul 19, 2023 at 2:44 AM EEST, Sean Christopherson wrote:quoted
/* Huge pages aren't expected to be modified without first being zapped. */ - WARN_ON(pte_huge(range->pte) || range->start + 1 != range->end); + WARN_ON(pte_huge(range->arg.pte) || range->start + 1 != range->end);Not familiar with this code. Just checking whether whether instead pr_{warn,err}()
The "full" WARN is desirable, this is effecitvely an assert on the contract between the primary MMU, generic KVM code, and x86's TDP MMU. The .change_pte() mmu_notifier callback doesn't allow for hugepages, i.e. it's a (likely fatal) kernel bug if a hugepage is encountered at this point. Ditto for the "start + 1 == end" check, if that fails then generic KVM likely has a fatal bug.
combined with return false would be a more graceful option?
The return value communicates whether or not a TLB flush is needed, not whether or not the operation was successful, i.e. there is no way to cancel the unexpected PTE change.