<!DOCTYPE html><html><head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> </head> <body> Am 16.01.25 um 02:46 schrieb Zhaoyang Huang: <blockquote type="cite" cite="mid:CAGWkznFPpU6uHQbgYrdwwWO8L-ct5nJoYnmdfqewxgNtMu2Qqg@mail.gmail.com"> <pre class="moz-quote-pre" wrap="">On Wed, Jan 15, 2025 at 7:49 PM Christian König <a class="moz-txt-link-rfc2396E" href="mailto:christian.koenig@amd.com"><christian.koenig@amd.com></a> wrote: </pre> <blockquote type="cite"> <pre class="moz-quote-pre" wrap=""> Am 15.01.25 um 07:18 schrieb zhaoyang.huang: </pre> <blockquote type="cite"> <pre class="moz-quote-pre" wrap="">From: Zhaoyang Huang <a class="moz-txt-link-rfc2396E" href="mailto:zhaoyang.huang@unisoc.com"><zhaoyang.huang@unisoc.com></a> When using dma-buf as memory pool for VMM. The vmf_insert_pfn will apply PTE_SPECIAL on pte which have vm_normal_page report bad_pte and return NULL. This commit would like to suggest to replace vmf_insert_pfn by vmf_insert_page. </pre> </blockquote> <pre class="moz-quote-pre" wrap=""> Setting PTE_SPECIAL is completely intentional here to prevent get_user_pages() from working on DMA-buf mappings. </pre> </blockquote> <pre class="moz-quote-pre" wrap="">ok. May I ask the reason?</pre> </blockquote> Drivers using this interface own the backing store for their specific use cases. There are a couple of things get_user_pages(), pin_user_pages(), direct I/O etc.. do which usually clash with those use cases. So that is intentionally completely disabled. We have the possibility to create a DMA-buf from memfd object and you can then do direct I/O to the memfd and still use the DMA-buf with GPUs or V4L for example. <blockquote type="cite" cite="mid:CAGWkznFPpU6uHQbgYrdwwWO8L-ct5nJoYnmdfqewxgNtMu2Qqg@mail.gmail.com"> <blockquote type="cite"> <pre class="moz-quote-pre" wrap=""> So absolutely clear NAK to this patch here. What exactly are you trying to do? </pre> </blockquote> <pre class="moz-quote-pre" wrap="">I would like to have pkvm have guest kernel be faulted of its second stage page fault(ARM64's memory virtualization method) on dma-buf which use pin_user_pages.</pre> </blockquote> Yeah, exactly that's one of the use case which we intentionally prevent here. The backing store drivers use don't care about the pin count of the memory and happily give it back to memory pools and/or swap it with device local memory if necessary. When this happens the ARM VM wouldn't be informed of the change and potentially accesses the wrong address. So sorry, but this approach won't work. You could try with the memfd+DMA-buf approach I mentioned earlier, but that won't give you all functionality on all DMA-buf supporting devices. For example GPUs usually can't scan out to a monitor from such buffers because of hardware limitations. Regards, Christian. <blockquote type="cite" cite="mid:CAGWkznFPpU6uHQbgYrdwwWO8L-ct5nJoYnmdfqewxgNtMu2Qqg@mail.gmail.com"> <pre class="moz-quote-pre" wrap=""> </pre> <blockquote type="cite"> <pre class="moz-quote-pre" wrap=""> Regards, Christian. </pre> <blockquote type="cite"> <pre class="moz-quote-pre" wrap=""> [ 103.402787] kvm [5276]: gfn(ipa)=0x80000 hva=0x7d4a400000 write_fault=0 [ 103.403822] BUG: Bad page map in process crosvm_vcpu0 pte:168000140000f43 pmd:8000000c1ca0003 [ 103.405144] addr:0000007d4a400000 vm_flags:040400fb anon_vma:0000000000000000 mapping:ffffff8085163df0 index:0 [ 103.406536] <a class="moz-txt-link-freetext" href="file:dmabuf">file:dmabuf</a> fault:cma_heap_vm_fault [cma_heap] mmap:dma_buf_mmap_internal read_folio:0x0 [ 103.407877] CPU: 3 PID: 5276 Comm: crosvm_vcpu0 Tainted: G W OE 6.6.46-android15-8-g8bab72b63c20-dirty-4k #1 1e474a12dac4553a3ebba3a911f3b744176a5d2d [ 103.409818] Hardware name: Unisoc UMS9632-base Board (DT) [ 103.410613] Call trace: [ 103.411038] dump_backtrace+0xf4/0x140 [ 103.411641] show_stack+0x20/0x30 [ 103.412184] dump_stack_lvl+0x60/0x84 [ 103.412766] dump_stack+0x18/0x24 [ 103.413304] print_bad_pte+0x1b8/0x1cc [ 103.413909] vm_normal_page+0xc8/0xd0 [ 103.414491] follow_page_pte+0xb0/0x304 [ 103.415096] follow_page_mask+0x108/0x240 [ 103.415721] __get_user_pages+0x168/0x4ac [ 103.416342] __gup_longterm_locked+0x15c/0x864 [ 103.417023] pin_user_pages+0x70/0xcc [ 103.417609] pkvm_mem_abort+0xf8/0x5c0 [ 103.418207] kvm_handle_guest_abort+0x3e0/0x3e4 [ 103.418906] handle_exit+0xac/0x33c [ 103.419472] kvm_arch_vcpu_ioctl_run+0x48c/0x8d8 [ 103.420176] kvm_vcpu_ioctl+0x504/0x5bc [ 103.420785] __arm64_sys_ioctl+0xb0/0xec [ 103.421401] invoke_syscall+0x60/0x11c [ 103.422000] el0_svc_common+0xb4/0xe8 [ 103.422590] do_el0_svc+0x24/0x30 [ 103.423131] el0_svc+0x3c/0x70 [ 103.423640] el0t_64_sync_handler+0x68/0xbc [ 103.424288] el0t_64_sync+0x1a8/0x1ac Signed-off-by: Xiwei Wang <a class="moz-txt-link-rfc2396E" href="mailto:xiwei.wang1@unisoc.com"><xiwei.wang1@unisoc.com></a> Signed-off-by: Aijun Sun <a class="moz-txt-link-rfc2396E" href="mailto:aijun.sun@unisoc.com"><aijun.sun@unisoc.com></a> Signed-off-by: Zhaoyang Huang <a class="moz-txt-link-rfc2396E" href="mailto:zhaoyang.huang@unisoc.com"><zhaoyang.huang@unisoc.com></a> --- drivers/dma-buf/heaps/cma_heap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/dma-buf/heaps/cma_heap.c b/drivers/dma-buf/heaps/cma_heap.c index c384004b918e..b301fb63f16b 100644 --- a/drivers/dma-buf/heaps/cma_heap.c +++ b/drivers/dma-buf/heaps/cma_heap.c @@ -168,7 +168,7 @@ static vm_fault_t cma_heap_vm_fault(struct vm_fault *vmf) if (vmf->pgoff > buffer->pagecount) return VM_FAULT_SIGBUS; - return vmf_insert_pfn(vma, vmf->address, page_to_pfn(buffer->pages[vmf->pgoff])); + return vmf_insert_page(vma, vmf->address, buffer->pages[vmf->pgoff]); } static const struct vm_operations_struct dma_heap_vm_ops = { </pre> </blockquote> <pre class="moz-quote-pre" wrap=""> </pre> </blockquote> </blockquote> </body> </html>