KVM: arm/arm64: Re-check VMA on detecting a poisoned page

When we check for a poisoned page, we use the VMA to tell userspace
about the looming disaster. But we pass a pointer to this VMA
after having released the mmap_sem, which isn't a good idea.

Instead, stash the shift value that goes with this pfn while
we are holding the mmap_sem.
Reported-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Christoffer Dall <christoffer.dall@arm.com>
Link: https://lore.kernel.org/r/20191211165651.7889-3-maz@kernel.org
Link: https://lore.kernel.org/r/20191217123809.197392-1-james.morse@arm.com

virt/kvm/arm/mmu.c

@@ -1596,16 +1596,8 @@ static void invalidate_icache_guest_page(kvm_pfn_t pfn, unsigned long size)
 	__invalidate_icache_guest_page(pfn, size);
 }
 
-static void kvm_send_hwpoison_signal(unsigned long address,
-				     struct vm_area_struct *vma)
+static void kvm_send_hwpoison_signal(unsigned long address, short lsb)
 {
-	short lsb;
-
-	if (is_vm_hugetlb_page(vma))
-		lsb = huge_page_shift(hstate_vma(vma));
-	else
-		lsb = PAGE_SHIFT;
-
 	send_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, lsb, current);
 }
 
@@ -1678,6 +1670,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 	struct kvm *kvm = vcpu->kvm;
 	struct kvm_mmu_memory_cache *memcache = &vcpu->arch.mmu_page_cache;
 	struct vm_area_struct *vma;
+	short vma_shift;
 	kvm_pfn_t pfn;
 	pgprot_t mem_type = PAGE_S2;
 	bool logging_active = memslot_is_logging(memslot);
@@ -1701,7 +1694,12 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 		return -EFAULT;
 	}
 
-	vma_pagesize = vma_kernel_pagesize(vma);
+	if (is_vm_hugetlb_page(vma))
+		vma_shift = huge_page_shift(hstate_vma(vma));
+	else
+		vma_shift = PAGE_SHIFT;
+
+	vma_pagesize = 1ULL << vma_shift;
 	if (logging_active ||
 	    (vma->vm_flags & VM_PFNMAP) ||
 	    !fault_supports_stage2_huge_mapping(memslot, hva, vma_pagesize)) {
@@ -1741,7 +1739,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 
 	pfn = gfn_to_pfn_prot(kvm, gfn, write_fault, &writable);
 	if (pfn == KVM_PFN_ERR_HWPOISON) {
-		kvm_send_hwpoison_signal(hva, vma);
+		kvm_send_hwpoison_signal(hva, vma_shift);
 		return 0;
 	}
 	if (is_error_noslot_pfn(pfn))