linux.git/arch/parisc/kernel/alternative.c, branch v6.8

parisc: Use num_present_cpus() in alternative patching code

2023-05-23T16:17:32+00:00

When patching the kernel code some alternatives depend on SMP vs. !SMP.
Use the value of num_present_cpus() instead of num_online_cpus() to
decide, otherwise we may run into issues if and additional CPU is
enabled after having loaded a module while only one CPU was enabled.

Signed-off-by: Helge Deller 
Cc:  # v6.1+

parisc: Reduce kernel size by packing alternative tables

2022-10-11T10:01:24+00:00

The values stored in the length and condition fields of the alternative
tables fit into 16 bits, so we can save 4 bytes per alternative table
entry.
Since a typical 32-bit kernel has more than 3000 entries this
saves > 12k of storage on disc.

bloat-o-meter shows a reduction of -0.01% by this change:
Total: Before=10196505, After=10195529, chg -0.01%

$ ls -la vmlinux vmlinux.before
-rwxr-xr-x  14437324 vmlinux
-rwxr-xr-x  14449512 vmlinux.before

Signed-off-by: Helge Deller

parisc: Avoid calling SMP cache flush functions on cache-less machines

2022-03-16T21:52:12+00:00

At least the qemu virtual machine does not provide D- and I-caches,
so skip triggering SMP irqs to flush caches on such machines.

Further optimize the caching code by using static branches and making
some functions static.

Signed-off-by: Helge Deller

parisc: Refactor alternative code to accept multiple conditions

2020-04-05T20:50:40+00:00

Allow the alternative loop to accept multiple conditions when replacing
existing code, e.g.
	ALTERNATIVE(ALT_COND_NO_SMP | ALT_COND_RUN_ON_QEMU, INSN_NOP)

Signed-off-by: Helge Deller

parisc: Add ALTERNATIVE_CODE() and ALT_COND_RUN_ON_QEMU

2019-08-12T17:17:39+00:00

The macro ALTERNATIVE_CODE() allows assembly code to patch in a series
of new assembler statements given at a specific start address.
The ALT_COND_RUN_ON_QEMU condition is true if the kernel is started in a
qemu emulation.

Signed-off-by: Helge Deller

parisc: Fix crash due alternative coding for NP iopdir_fdc bit

2019-06-06T12:25:22+00:00

According to the found documentation, data cache flushes and sync
instructions are needed on the PCX-U+ (PA8200, e.g. C200/C240)
platforms, while PCX-W (PA8500, e.g. C360) platforms aparently don't
need those flushes when changing the IO PDIR data structures.

We have no documentation for PCX-W+ (PA8600) and PCX-W2 (PA8700) CPUs,
but Carlo Pisani reported that his C3600 machine (PA8600, PCX-W+) fails
when the fdc instructions were removed. His firmware didn't set the NIOP
bit, so one may assume it's a firmware bug since other C3750 machines
had the bit set.

Even if documentation (as mentioned above) states that PCX-W (PA8500,
e.g.  J5000) does not need fdc flushes, Sven could show that an Adaptec
29320A PCI-X SCSI controller reliably failed on a dd command during the
first five minutes in his J5000 when fdc flushes were missing.

Going forward, we will now NOT replace the fdc and sync assembler
instructions by NOPS if:
a) the NP iopdir_fdc bit was set by firmware, or
b) we find a CPU up to and including a PCX-W+ (PA8600).

This fixes the HPMC crashes on a C240 and C36XX machines. For other
machines we rely on the firmware to set the bit when needed.

In case one finds HPMC issues, people could try to boot their machines
with the "no-alternatives" kernel option to turn off any alternative
patching.

Reported-by: Sven Schnelle 
Reported-by: Carlo Pisani 
Tested-by: Sven Schnelle 
Fixes: 3847dab77421 ("parisc: Add alternative coding infrastructure")
Signed-off-by: Helge Deller 
Cc: stable@vger.kernel.org # 5.0+

parisc: Split out alternative live patching code

2018-12-10T06:47:50+00:00

Move the alternative implemenation coding to alternative.c and add code to
patch modules while loading.

Signed-off-by: Helge Deller