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Filename Latest commit message Latest commit date
Dexuan Cui 9e60056b1f video: hyperv_fb: Fix the mmap() regression for v5.4.y and older 
db49200b1d is backported from the mainline commit
5f1251a48c17 ("video: hyperv_fb: Fix the cache type when mapping the VRAM"),
to v5.4.y and older stable branches, but unluckily db49200b1d causes
mmap() to fail for /dev/fb0 due to EINVAL:

[ 5797.049560] x86/PAT: a.out:1910 map pfn expected mapping type
  uncached-minus for [mem 0xf8200000-0xf85cbfff], got write-back

This means the v5.4.y kernel detects an incompatibility issue about the
mapping type of the VRAM: db49200b1d changes to use Write-Back when
mapping the VRAM, while the mmap() syscall tries to use Uncached-minus.
That’s to say, the kernel thinks Uncached-minus is incompatible with
Write-Back: see drivers/video/fbdev/core/fbmem.c: fb_mmap() ->
vm_iomap_memory() -> io_remap_pfn_range() -> ... -> track_pfn_remap() ->
reserve_pfn_range().

Note: any v5.5 and newer kernel doesn't have the issue, because they
have commit
d21987d709e8 ("video: hyperv: hyperv_fb: Support deferred IO for Hyper-V frame buffer driver")
, and when the hyperv_fb driver has the deferred_io support,
fb_deferred_io_init() overrides info->fbops->fb_mmap with
fb_deferred_io_mmap(), which doesn’t check the mapping type
incompatibility. Note: since it's VRAM here, the checking is not really
necessary.

Fix the regression by ioremap_wc(), which uses Write-combining. The kernel
thinks it's compatible with Uncached-minus. The VRAM mappped by
ioremap_wc() is slightly slower than mapped by ioremap_cache(), but is
still significantly faster than by ioremap().

Change the comment accordingly. Linux VM on ARM64 Hyper-V is still not
working in the latest mainline yet, and when it works in future, the ARM64
support is unlikely to be backported to v5.4 and older, so using
ioremap_wc() in v5.4 and older should be ok.

Note: this fix is only targeted at the stable branches:
v5.4.y, v4.19.y, v4.14.y, v4.9.y and v4.4.y.

Fixes: db49200b1d ("video: hyperv_fb: Fix the cache type when mapping the VRAM")
Signed-off-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2021-01-12 20:16:17 +01:00
arch um: ubd: Submit all data segments atomically 2021-01-06 14:48:40 +01:00
block scsi: block: Fix a race in the runtime power management code 2021-01-06 14:48:37 +01:00
certs
crypto crypto: ecdh - avoid unaligned accesses in ecdh_set_secret() 2020-12-30 11:51:35 +01:00
Documentation x86/CPU/AMD: Save AMD NodeId as cpu_die_id 2020-12-30 11:51:47 +01:00
drivers video: hyperv_fb: Fix the mmap() regression for v5.4.y and older 2021-01-12 20:16:17 +01:00
fs proc: fix lookup in /proc/net subdirectories after setns(2) 2021-01-12 20:16:10 +01:00
include net: sched: prevent invalid Scell_log shift count 2021-01-12 20:16:14 +01:00
init exec: Transform exec_update_mutex into a rw_semaphore 2021-01-09 13:44:55 +01:00
ipc
kernel workqueue: Kick a worker based on the actual activation of delayed works 2021-01-12 20:16:09 +01:00
lib lib/genalloc: fix the overflow when size is too big 2021-01-12 20:16:10 +01:00
LICENSES
mm mm: don't wake kswapd prematurely when watermark boosting is disabled 2020-12-30 11:51:27 +01:00
net net/sched: sch_taprio: ensure to reset/destroy all child qdiscs 2021-01-12 20:16:16 +01:00
samples samples: bpf: Fix lwt_len_hist reusing previous BPF map 2020-12-30 11:51:12 +01:00
scripts depmod: handle the case of /sbin/depmod without /sbin in PATH 2021-01-12 20:16:10 +01:00
security ima: Don't modify file descriptor mode on the fly 2020-12-30 11:51:39 +01:00
sound ALSA: pcm: Clear the full allocated memory at hw_params 2021-01-06 14:48:40 +01:00
tools tools headers UAPI: Sync linux/const.h with the kernel headers 2021-01-06 14:48:37 +01:00
usr
virt KVM: arm64: vgic-v3: Drop the reporting of GICR_TYPER.Last for userspace 2020-12-02 08:49:46 +01:00
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore
.mailmap
COPYING
CREDITS
Kbuild
Kconfig
MAINTAINERS Documentation/llvm: add documentation on building w/ Clang/LLVM 2020-08-26 10:40:46 +02:00
Makefile kbuild: don't hardcode depmod path 2021-01-12 20:16:16 +01:00
README

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.