linux-kernel - Re: [RFC PATCH] driver: dma-buf: use vmf_insert_page for cma_heap_vm

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Message-ID: <CAGWkznFPpU6uHQbgYrdwwWO8L-ct5nJoYnmdfqewxgNtMu2Qqg@mail.gmail.com>
Date: Thu, 16 Jan 2025 09:46:39 +0800
From: Zhaoyang Huang <huangzhaoyang@...il.com>
To: Christian König <christian.koenig@....com>
Cc: "zhaoyang.huang" <zhaoyang.huang@...soc.com>, Sumit Semwal <sumit.semwal@...aro.org>, 
	Benjamin Gaignard <benjamin.gaignard@...labora.com>, Brian Starkey <Brian.Starkey@....com>, 
	John Stultz <jstultz@...gle.com>, "T . J . Mercier" <tjmercier@...gle.com>, 
	"open list:DMA-BUF HEAPS FRAMEWORK" <linux-media@...r.kernel.org>, 
	"open list:DMA-BUF HEAPS FRAMEWORK" <dri-devel@...ts.freedesktop.org>, 
	"moderated list:DMA-BUF HEAPS FRAMEWORK" <linaro-mm-sig@...ts.linaro.org>, linux-kernel@...r.kernel.org, 
	steve.kang@...soc.com
Subject: Re: [RFC PATCH] driver: dma-buf: use vmf_insert_page for cma_heap_vm_fault

On Wed, Jan 15, 2025 at 7:49 PM Christian König
<christian.koenig@....com> wrote:
>
> Am 15.01.25 um 07:18 schrieb zhaoyang.huang:
> > From: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> >
> > 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.
>
> Setting PTE_SPECIAL is completely intentional here to prevent
> get_user_pages() from working on DMA-buf mappings.
ok. May I ask the reason?
>
> So absolutely clear NAK to this patch here.
>
> What exactly are you trying to do?
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.
>
> Regards,
> Christian.
>
> >
> > [  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] file:dmabuf 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 <xiwei.wang1@...soc.com>
> > Signed-off-by: Aijun Sun <aijun.sun@...soc.com>
> > Signed-off-by: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> > ---
> >   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 = {
>