linux-toradex.git/arch/powerpc/kernel, branch v4.9.88

powerpc/64s: Improve RFI L1-D cache flush fallback

2018-02-25T10:05:50+00:00

commit bdcb1aefc5b3f7d0f1dc8b02673602bca2ff7a4b upstream.

The fallback RFI flush is used when firmware does not provide a way
to flush the cache. It's a "displacement flush" that evicts useful
data by displacing it with an uninteresting buffer.

The flush has to take care to work with implementation specific cache
replacment policies, so the recipe has been in flux. The initial
slow but conservative approach is to touch all lines of a congruence
class, with dependencies between each load. It has since been
determined that a linear pattern of loads without dependencies is
sufficient, and is significantly faster.

Measuring the speed of a null syscall with RFI fallback flush enabled
gives the relative improvement:

P8 - 1.83x
P9 - 1.75x

The flush also becomes simpler and more adaptable to different cache
geometries.

Signed-off-by: Nicholas Piggin 
[mpe: Backport to 4.9]
Signed-off-by: Michael Ellerman 
Signed-off-by: Greg Kroah-Hartman

powerpc/64s: Simple RFI macro conversions

2018-02-25T10:05:50+00:00

commit 222f20f140623ef6033491d0103ee0875fe87d35 upstream.

This commit does simple conversions of rfi/rfid to the new macros that
include the expected destination context. By simple we mean cases
where there is a single well known destination context, and it's
simply a matter of substituting the instruction for the appropriate
macro.

Signed-off-by: Nicholas Piggin 
[mpe: Backport to 4.9, use RFI_TO_KERNEL in idle_book3s.S]
Signed-off-by: Michael Ellerman 
Signed-off-by: Greg Kroah-Hartman

powerpc/64s: Fix conversion of slb_miss_common to use RFI_TO_USER/KERNEL

2018-02-25T10:05:50+00:00

The back port of commit c7305645eb0c ("powerpc/64s: Convert
slb_miss_common to use RFI_TO_USER/KERNEL") missed a hunk needed to
restore cr6.

Fixes: 48cc95d4e4d6 ("powerpc/64s: Convert slb_miss_common to use RFI_TO_USER/KERNEL")
Signed-off-by: Michael Ellerman 
Signed-off-by: Greg Kroah-Hartman

powerpc: fix build errors in stable tree

2018-02-22T14:43:51+00:00

This is just the first chunk of commit
222f20f140623ef6033491d0103ee0875fe87d35 upstream.

to fix a build error in the powerpc tree due to other backports
happening (and this full patch not being backported).

Reported-by: Guenter Roeck 
Reported-by: Yves-Alexis Perez 
Cc: Nicholas Piggin 
Cc: Michael Ellerman 
Cc: Yves-Alexis Perez 
Signed-off-by: Greg Kroah-Hartman

powerpc/64s: Allow control of RFI flush via debugfs

2018-02-13T11:35:55+00:00

commit 236003e6b5443c45c18e613d2b0d776a9f87540e upstream.

Expose the state of the RFI flush (enabled/disabled) via debugfs, and
allow it to be enabled/disabled at runtime.

eg: $ cat /sys/kernel/debug/powerpc/rfi_flush
    1
    $ echo 0 > /sys/kernel/debug/powerpc/rfi_flush
    $ cat /sys/kernel/debug/powerpc/rfi_flush
    0

Signed-off-by: Michael Ellerman 
Reviewed-by: Nicholas Piggin 
Signed-off-by: Greg Kroah-Hartman

powerpc/64s: Wire up cpu_show_meltdown()

2018-02-13T11:35:55+00:00

commit fd6e440f20b1a4304553775fc55938848ff617c9 upstream.

The recent commit 87590ce6e373 ("sysfs/cpu: Add vulnerability folder")
added a generic folder and set of files for reporting information on
CPU vulnerabilities. One of those was for meltdown:

  /sys/devices/system/cpu/vulnerabilities/meltdown

This commit wires up that file for 64-bit Book3S powerpc.

For now we default to "Vulnerable" unless the RFI flush is enabled.
That may not actually be true on all hardware, further patches will
refine the reporting based on the CPU/platform etc. But for now we
default to being pessimists.

Signed-off-by: Michael Ellerman 
Signed-off-by: Greg Kroah-Hartman

powerpc/64s: Support disabling RFI flush with no_rfi_flush and nopti

2018-02-13T11:35:54+00:00

commit bc9c9304a45480797e13a8e1df96ffcf44fb62fe upstream.

Because there may be some performance overhead of the RFI flush, add
kernel command line options to disable it.

We add a sensibly named 'no_rfi_flush' option, but we also hijack the
x86 option 'nopti'. The RFI flush is not the same as KPTI, but if we
see 'nopti' we can guess that the user is trying to avoid any overhead
of Meltdown mitigations, and it means we don't have to educate every
one about a different command line option.

Signed-off-by: Michael Ellerman 
Signed-off-by: Greg Kroah-Hartman

powerpc/64s: Add support for RFI flush of L1-D cache

2018-02-13T11:35:54+00:00

commit aa8a5e0062ac940f7659394f4817c948dc8c0667 upstream.

On some CPUs we can prevent the Meltdown vulnerability by flushing the
L1-D cache on exit from kernel to user mode, and from hypervisor to
guest.

This is known to be the case on at least Power7, Power8 and Power9. At
this time we do not know the status of the vulnerability on other CPUs
such as the 970 (Apple G5), pasemi CPUs (AmigaOne X1000) or Freescale
CPUs. As more information comes to light we can enable this, or other
mechanisms on those CPUs.

The vulnerability occurs when the load of an architecturally
inaccessible memory region (eg. userspace load of kernel memory) is
speculatively executed to the point where its result can influence the
address of a subsequent speculatively executed load.

In order for that to happen, the first load must hit in the L1,
because before the load is sent to the L2 the permission check is
performed. Therefore if no kernel addresses hit in the L1 the
vulnerability can not occur. We can ensure that is the case by
flushing the L1 whenever we return to userspace. Similarly for
hypervisor vs guest.

In order to flush the L1-D cache on exit, we add a section of nops at
each (h)rfi location that returns to a lower privileged context, and
patch that with some sequence. Newer firmwares are able to advertise
to us that there is a special nop instruction that flushes the L1-D.
If we do not see that advertised, we fall back to doing a displacement
flush in software.

For guest kernels we support migration between some CPU versions, and
different CPUs may use different flush instructions. So that we are
prepared to migrate to a machine with a different flush instruction
activated, we may have to patch more than one flush instruction at
boot if the hypervisor tells us to.

In the end this patch is mostly the work of Nicholas Piggin and
Michael Ellerman. However a cast of thousands contributed to analysis
of the issue, earlier versions of the patch, back ports testing etc.
Many thanks to all of them.

Tested-by: Jon Masters 
Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
[Balbir - back ported to stable with changes]
Signed-off-by: Balbir Singh 
Signed-off-by: Greg Kroah-Hartman

powerpc/64s: Convert slb_miss_common to use RFI_TO_USER/KERNEL

2018-02-13T11:35:54+00:00

commit c7305645eb0c1621351cfc104038831ae87c0053 upstream.

In the SLB miss handler we may be returning to user or kernel. We need
to add a check early on and save the result in the cr4 register, and
then we bifurcate the return path based on that.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Signed-off-by: Nicholas Piggin 
[mpe: Backport to 4.4 based on patch from Balbir]
Signed-off-by: Michael Ellerman 
Signed-off-by: Greg Kroah-Hartman

powerpc/64: Convert the syscall exit path to use RFI_TO_USER/KERNEL

2018-02-13T11:35:54+00:00

commit b8e90cb7bc04a509e821e82ab6ed7a8ef11ba333 upstream.

In the syscall exit path we may be returning to user or kernel
context. We already have a test for that, because we conditionally
restore r13. So use that existing test and branch, and bifurcate the
return based on that.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Signed-off-by: Greg Kroah-Hartman