[PATCH bpf-next v5 1/3] btf: allow mmap of vmlinux btf

[Breno Leitao]

Hello Lorenz,

On Tue, May 20, 2025 at 02:01:17PM +0100, Lorenz Bauer wrote:
> diff --git a/kernel/bpf/sysfs_btf.c b/kernel/bpf/sysfs_btf.c
> index 81d6cf90584a7157929c50f62a5c6862e7a3d081..941d0d2427e3a2d27e8f1cff7b6424d0d41817c1 100644
> --- a/kernel/bpf/sysfs_btf.c
> +++ b/kernel/bpf/sysfs_btf.c

>  extern char __start_BTF[];
>  extern char __stop_BTF[];

> +static int btf_sysfs_vmlinux_mmap(struct file *filp, struct kobject *kobj,
> +				  const struct bin_attribute *attr,
> +				  struct vm_area_struct *vma)
> +{
> +	unsigned long pages = PAGE_ALIGN(attr->size) >> PAGE_SHIFT;
> +	size_t vm_size = vma->vm_end - vma->vm_start;
> +	phys_addr_t addr = virt_to_phys(__start_BTF);

I am getting the following warning on arm64 which seems related to this
code here. lines are based on cd031354087d8ae ("Merge branch
'net-mlx5e-add-support-for-pcie-congestion-events') net-next branch

	[   58.896157] virt_to_phys used for non-linear address: 000000009fea9737 (__start_BTF+0x0/0x685530)
	[   23.988669] WARNING: CPU: 25 PID: 1442 at arch/arm64/mm/physaddr.c:15 __virt_to_phys (arch/arm64/mm/physaddr.c:?)
	[   24.018136] Modules linked in: nvidia_cspmu(E) mlx5_ib(E) ipmi_ssif(E) arm_smmuv3_pmu(E) arm_cspmu_module(E) coresight_trbe(E) ib_uverbs(E) ipmi_devintf(E) ipmi_msghandler(E) coresight_stm(E) coresight_etm4x(E) coresight_tmc(E) coresight_funnel(E) stm_core(E) coresight(E) cppc_cpufreq(E) sch_fq_codel(E) drm(E) backlight(E) drm_panel_orientation_quirks(E) xhci_pci(E) xhci_hcd(E) sm3_ce(E) sha3_ce(E) sha512_ce(E) spi_tegra210_quad(E) acpi_power_meter(E) loop(E) efivarfs(E) autofs4(E)
	[   24.075371] Tainted: [E]=UNSIGNED_MODULE, [N]=TEST
	[   24.080276] Hardware name: Quanta S7GM 20S7GCU0010/S7G MB (CG1), BIOS 3D22 07/03/2024
	[   24.088295] pstate: 63400009 (nZCv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
	[   24.098440] pc : __virt_to_phys (arch/arm64/mm/physaddr.c:?)
	[   24.105398] lr : __virt_to_phys (arch/arm64/mm/physaddr.c:?)
	[   24.112227] sp : ffff8000ba00f8e0
	[   24.115620] x29: ffff8000ba00f8e0 x28: ffff8000ba00faf0 x27: ffff8000ba00fa88
	[   24.122919] x26: ffff8000ba00fa40 x25: ffff800082772000 x24: 0000fffd6db70000
	[   24.130226] x23: 0000000000685530 x22: 0000fffd6e200000 x21: ffff800081cc0000
	[   24.140540] x20: ffff800081be02d8 x19: ffff800081cc0000 x18: 5f5f282037333739
	[   24.150708] x17: 6165663930303030 x16: 0000000000000fc4 x15: 0000000000000003
	[   24.160737] x14: ffff800082923398 x13: 0000000000000003 x12: 0000000000000003
	[   24.168042] x11: 00000000fffeffff x10: ffff800082663784 x9 : cc38fcac5cdabe00
	[   24.175348] x8 : 0001000000000000 x7 : ffff8000813dd878 x6 : 0000000000000000
	[   24.182653] x5 : 0000000000000001 x4 : 0000000000000001 x3 : 0000000000000000
	[   24.189959] x2 : 0000000000000000 x1 : ffff800081a3a6d0 x0 : 0000000000000055
	[   24.197257] Call trace:
	[   24.199761] __virt_to_phys (arch/arm64/mm/physaddr.c:?) (P)
	[   24.206883] btf_sysfs_vmlinux_mmap (kernel/bpf/sysfs_btf.c:27)
	[   24.214264] sysfs_kf_bin_mmap (fs/sysfs/file.c:179)
	[   24.218536] kernfs_fop_mmap (fs/kernfs/file.c:462)
	[   24.222461] mmap_region (./include/linux/fs.h:? mm/internal.h:167 mm/vma.c:2405 mm/vma.c:2467 mm/vma.c:2622 mm/vma.c:2692)


Should __pa_symbol() be used instead of virt_to_phys()?

Thanks
--breno