Re: [PATCH v1] riscv: mm: Skip the icache flush for special PTEs

[Karl Mehltretter <kmehltretter@gmail.com>]

On Fri, Oct 16, 2026 at 09:36:34PM -0400, Nickolai Zeldovich wrote:
> Mapping device memory executable crashes the kernel: an mmap() with
> PROT_EXEC of a physical range outside RAM, from /dev/mem, from a PCI
> BAR's sysfs resource file, from a frame buffer or from any driver whose
> mmap() uses remap_pfn_range(), io_remap_pfn_range() or vmf_insert_pfn(),
> oopses in flush_icache_pte() with the page table lock held

I hit the same oops on QEMU virt with an executable /dev/mem mapping of
0x200000, which is unassigned there. The kernel was abf8c33470f7 with
riscv64 defconfig and OpenSBI v1.8.1. The mmap() oopses in
flush_icache_pte() called from do_remap_pfn_range(), and init dies.

With this patch the mapping succeeds. Loads, stores and instruction
fetches through it raise access faults, which reach user space as
SIGSEGV.

Tested-by: Karl Mehltretter <kmehltretter@gmail.com>

Thanks,
Karl