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Peter Anvin" , Brijesh Singh , Michael Roth , Ashish Kalra , kvm@vger.kernel.org, linux-kernel@vger.kernel.org References: <20240612115040.2423290-2-dan.carpenter@linaro.org> <20240612115040.2423290-4-dan.carpenter@linaro.org> From: Paolo Bonzini Content-Language: en-US Autocrypt: addr=pbonzini@redhat.com; keydata= xsEhBFRCcBIBDqDGsz4K0zZun3jh+U6Z9wNGLKQ0kSFyjN38gMqU1SfP+TUNQepFHb/Gc0E2 CxXPkIBTvYY+ZPkoTh5xF9oS1jqI8iRLzouzF8yXs3QjQIZ2SfuCxSVwlV65jotcjD2FTN04 hVopm9llFijNZpVIOGUTqzM4U55sdsCcZUluWM6x4HSOdw5F5Utxfp1wOjD/v92Lrax0hjiX DResHSt48q+8FrZzY+AUbkUS+Jm34qjswdrgsC5uxeVcLkBgWLmov2kMaMROT0YmFY6A3m1S P/kXmHDXxhe23gKb3dgwxUTpENDBGcfEzrzilWueOeUWiOcWuFOed/C3SyijBx3Av/lbCsHU Vx6pMycNTdzU1BuAroB+Y3mNEuW56Yd44jlInzG2UOwt9XjjdKkJZ1g0P9dwptwLEgTEd3Fo UdhAQyRXGYO8oROiuh+RZ1lXp6AQ4ZjoyH8WLfTLf5g1EKCTc4C1sy1vQSdzIRu3rBIjAvnC tGZADei1IExLqB3uzXKzZ1BZ+Z8hnt2og9hb7H0y8diYfEk2w3R7wEr+Ehk5NQsT2MPI2QBd wEv1/Aj1DgUHZAHzG1QN9S8wNWQ6K9DqHZTBnI1hUlkp22zCSHK/6FwUCuYp1zcAEQEAAc0j UGFvbG8gQm9uemluaSA8cGJvbnppbmlAcmVkaGF0LmNvbT7CwU0EEwECACMFAlRCcBICGwMH CwkIBwMCAQYVCAIJCgsEFgIDAQIeAQIXgAAKCRB+FRAMzTZpsbceDp9IIN6BIA0Ol7MoB15E 11kRz/ewzryFY54tQlMnd4xxfH8MTQ/mm9I482YoSwPMdcWFAKnUX6Yo30tbLiNB8hzaHeRj jx12K+ptqYbg+cevgOtbLAlL9kNgLLcsGqC2829jBCUTVeMSZDrzS97ole/YEez2qFpPnTV0 VrRWClWVfYh+JfzpXmgyhbkuwUxNFk421s4Ajp3d8nPPFUGgBG5HOxzkAm7xb1cjAuJ+oi/K CHfkuN+fLZl/u3E/fw7vvOESApLU5o0icVXeakfSz0LsygEnekDbxPnE5af/9FEkXJD5EoYG SEahaEtgNrR4qsyxyAGYgZlS70vkSSYJ+iT2rrwEiDlo31MzRo6Ba2FfHBSJ7lcYdPT7bbk9 AO3hlNMhNdUhoQv7M5HsnqZ6unvSHOKmReNaS9egAGdRN0/GPDWr9wroyJ65ZNQsHl9nXBqE AukZNr5oJO5vxrYiAuuTSd6UI/xFkjtkzltG3mw5ao2bBpk/V/YuePrJsnPFHG7NhizrxttB nTuOSCMo45pfHQ+XYd5K1+Cv/NzZFNWscm5htJ0HznY+oOsZvHTyGz3v91pn51dkRYN0otqr bQ4tlFFuVjArBZcapSIe6NV8C4cEiSTOwE0EVEJx7gEIAMeHcVzuv2bp9HlWDp6+RkZe+vtl KwAHplb/WH59j2wyG8V6i33+6MlSSJMOFnYUCCL77bucx9uImI5nX24PIlqT+zasVEEVGSRF m8dgkcJDB7Tps0IkNrUi4yof3B3shR+vMY3i3Ip0e41zKx0CvlAhMOo6otaHmcxr35sWq1Jk tLkbn3wG+fPQCVudJJECvVQ//UAthSSEklA50QtD2sBkmQ14ZryEyTHQ+E42K3j2IUmOLriF dNr9NvE1QGmGyIcbw2NIVEBOK/GWxkS5+dmxM2iD4Jdaf2nSn3jlHjEXoPwpMs0KZsgdU0pP JQzMUMwmB1wM8JxovFlPYrhNT9MAEQEAAcLBMwQYAQIACQUCVEJx7gIbDAAKCRB+FRAMzTZp sadRDqCctLmYICZu4GSnie4lKXl+HqlLanpVMOoFNnWs9oRP47MbE2wv8OaYh5pNR9VVgyhD OG0AU7oidG36OeUlrFDTfnPYYSF/mPCxHttosyt8O5kabxnIPv2URuAxDByz+iVbL+RjKaGM GDph56ZTswlx75nZVtIukqzLAQ5fa8OALSGum0cFi4ptZUOhDNz1onz61klD6z3MODi0sBZN Aj6guB2L/+2ZwElZEeRBERRd/uommlYuToAXfNRdUwrwl9gRMiA0WSyTb190zneRRDfpSK5d usXnM/O+kr3Dm+Ui+UioPf6wgbn3T0o6I5BhVhs4h4hWmIW7iNhPjX1iybXfmb1gAFfjtHfL xRUr64svXpyfJMScIQtBAm0ihWPltXkyITA92ngCmPdHa6M1hMh4RDX+Jf1fiWubzp1voAg0 JBrdmNZSQDz0iKmSrx8xkoXYfA3bgtFN8WJH2xgFL28XnqY4M6dLhJwV3z08tPSRqYFm4NMP dRsn0/7oymhneL8RthIvjDDQ5ktUjMe8LtHr70OZE/TT88qvEdhiIVUogHdo4qBrk41+gGQh b906Dudw5YhTJFU3nC6bbF2nrLlB4C/XSiH76ZvqzV0Z/cAMBo5NF/w= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 8/13/24 09:51, Dan Carpenter wrote: > On Mon, Aug 12, 2024 at 09:04:24PM -0700, Sean Christopherson wrote: >> On Wed, Jun 12, 2024, Dan Carpenter wrote: >>> The copy_from_user() function returns the number of bytes which it >>> was not able to copy. Return -EFAULT instead. >> >> Unless I'm misreading the code and forgetting how all this works, this is >> intentional. The direct caller treats any non-zero value as a error: >> >> ret = post_populate(kvm, gfn, pfn, p, max_order, opaque); >> >> put_page(pfn_to_page(pfn)); >> if (ret) >> break; >> } >> >> filemap_invalidate_unlock(file->f_mapping); >> >> fput(file); >> return ret && !i ? ret : i; >> > > No, you're not reading this correctly. The loop is supposed to return the > number of pages which were handled successfully. So this is saying that if the > first iteration fails and then return a negative error code. But with the bug > then if the first iteration fails, it returns the number of bytes which failed. Yes, you're supposed to return 0 or -errno, so that you return -errno on the first round. Applying the patches, 1/2 is also a bugfix even if the printks may be overkill. Thanks for the report! Paolo > The units are wrong pages vs bytes and the failure vs success is reversed. > > Also I notice now that i isn't correct unless we hit a break statement: > > virt/kvm/guest_memfd.c > 647 npages = min_t(ulong, slot->npages - (start_gfn - slot->base_gfn), npages); > > If there isn't enough pages, we use what's available. > > 648 for (i = 0; i < npages; i += (1 << max_order)) { > > If we exit because i >= npages then we return success as if we were able to > complete one final iteration through the loop. > > 649 struct folio *folio; > 650 gfn_t gfn = start_gfn + i; > 651 bool is_prepared = false; > 652 kvm_pfn_t pfn; > 653 > 654 if (signal_pending(current)) { > 655 ret = -EINTR; > 656 break; > 657 } > 658 > 659 folio = __kvm_gmem_get_pfn(file, slot, gfn, &pfn, &is_prepared, &max_order); > 660 if (IS_ERR(folio)) { > 661 ret = PTR_ERR(folio); > 662 break; > 663 } > 664 > 665 if (is_prepared) { > 666 folio_unlock(folio); > 667 folio_put(folio); > 668 ret = -EEXIST; > 669 break; > 670 } > 671 > 672 folio_unlock(folio); > 673 WARN_ON(!IS_ALIGNED(gfn, 1 << max_order) || > 674 (npages - i) < (1 << max_order)); > 675 > 676 ret = -EINVAL; > 677 while (!kvm_range_has_memory_attributes(kvm, gfn, gfn + (1 << max_order), > 678 KVM_MEMORY_ATTRIBUTE_PRIVATE, > 679 KVM_MEMORY_ATTRIBUTE_PRIVATE)) { > 680 if (!max_order) > 681 goto put_folio_and_exit; > 682 max_order--; > 683 } > 684 > 685 p = src ? src + i * PAGE_SIZE : NULL; > 686 ret = post_populate(kvm, gfn, pfn, p, max_order, opaque); > ^^^^^^^^^^^^^^^^^^^^ > post_populate() is a pointer to sev_gmem_post_populate() which has is supposed > to return negative error codes but instead returns number of bytes which failed. > > 687 if (!ret) > 688 kvm_gmem_mark_prepared(folio); > 689 > 690 put_folio_and_exit: > 691 folio_put(folio); > 692 if (ret) > 693 break; > 694 } > 695 > 696 filemap_invalidate_unlock(file->f_mapping); > 697 > 698 fput(file); > 699 return ret && !i ? ret : i; > 700 } > > regards, > dan carpenter > >