• Dave Airlie's avatar
    x86/io: add interface to reserve io memtype for a resource range. (v1.1) · 8ef42276
    Dave Airlie authored
    A recent change to the mm code in:
    87744ab3 mm: fix cache mode tracking in vm_insert_mixed()
    
    started enforcing checking the memory type against the registered list for
    amixed pfn insertion mappings. It happens that the drm drivers for a number
    of gpus relied on this being broken. Currently the driver only inserted
    VRAM mappings into the tracking table when they came from the kernel,
    and userspace mappings never landed in the table. This led to a regression
    where all the mapping end up as UC instead of WC now.
    
    I've considered a number of solutions but since this needs to be fixed
    in fixes and not next, and some of the solutions were going to introduce
    overhead that hadn't been there before I didn't consider them viable at
    this stage. These mainly concerned hooking into the TTM io reserve APIs,
    but these API have a bunch of fast paths I didn't want to unwind to add
    this to.
    
    The solution I've decided on is to add a new API like the arch_phys_wc
    APIs (these would have worked but wc_del didn't take a range), and
    use them from the drivers to add a WC compatible mapping to the table
    for all VRAM on those GPUs. This means we can then create userspace
    mapping that won't get degraded to UC.
    
    v1.1: use CONFIG_X86_PAT + add some comments in io.h
    
    Cc: Toshi Kani <toshi.kani@hp.com>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Denys Vlasenko <dvlasenk@redhat.com>
    Cc: Brian Gerst <brgerst@gmail.com>
    Cc: x86@kernel.org
    Cc: mcgrof@suse.com
    Cc: Dan Williams <dan.j.williams@intel.com>
    Acked-by: default avatarIngo Molnar <mingo@kernel.org>
    Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Signed-off-by: default avatarDave Airlie <airlied@redhat.com>
    8ef42276
io.h 4.96 KB