KVM: PPC: Book3S HV: Remove user-triggerable WARN_ON
Although in general we do not expect valid PTEs to be found in kvmppc_create_pte when we are inserting a large page mapping, there is one situation where this can occur. That is when dirty page logging is turned off for a memslot while the VM is running. Because the new memslots are installed before the old memslot is flushed in kvmppc_core_commit_memory_region_hv(), there is a window where a hypervisor page fault can try to install a 2MB (or 1GB) page where there are already small page mappings which were installed while dirty page logging was enabled and which have not yet been flushed. Since we have a situation where valid PTEs can legitimately be found by kvmppc_unmap_free_pte, and which can be triggered by userspace, just remove the WARN_ON_ONCE, since it is undesirable to have userspace able to trigger a kernel warning. Signed-off-by: Paul Mackerras <paulus@ozlabs.org>alistair/sunxi64-5.8
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@ -429,9 +429,13 @@ void kvmppc_unmap_pte(struct kvm *kvm, pte_t *pte, unsigned long gpa,
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* Callers are responsible for flushing the PWC.
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*
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* When page tables are being unmapped/freed as part of page fault path
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* (full == false), ptes are not expected. There is code to unmap them
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* and emit a warning if encountered, but there may already be data
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* corruption due to the unexpected mappings.
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* (full == false), valid ptes are generally not expected; however, there
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* is one situation where they arise, which is when dirty page logging is
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* turned off for a memslot while the VM is running. The new memslot
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* becomes visible to page faults before the memslot commit function
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* gets to flush the memslot, which can lead to a 2MB page mapping being
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* installed for a guest physical address where there are already 64kB
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* (or 4kB) mappings (of sub-pages of the same 2MB page).
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*/
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static void kvmppc_unmap_free_pte(struct kvm *kvm, pte_t *pte, bool full,
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unsigned int lpid)
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@ -445,7 +449,6 @@ static void kvmppc_unmap_free_pte(struct kvm *kvm, pte_t *pte, bool full,
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for (it = 0; it < PTRS_PER_PTE; ++it, ++p) {
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if (pte_val(*p) == 0)
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continue;
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WARN_ON_ONCE(1);
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kvmppc_unmap_pte(kvm, p,
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pte_pfn(*p) << PAGE_SHIFT,
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PAGE_SHIFT, NULL, lpid);
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