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docs: powerpc: convert docs to ReST and rename to *.rst Convert docs to ReST and add them to the arch-specific book. The conversion here was trivial, as almost every file there was already using an elegant format close to ReST standard. The changes were mostly to mark literal blocks and add a few missing section title identifiers. One note with regards to "--": on Sphinx, this can't be used to identify a list, as it will format it badly. This can be used, however, to identify a long hyphen - and "---" is an even longer one. At its new index.rst, let's add a :orphan: while this is not linked to the main index.rst file, in order to avoid build warnings. Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Acked-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com> # cxl
2019-04-10 04:32:42 -07:00
=====================
powerpc: Document issues with the DAWR on POWER9 Signed-off-by: Michael Neuling <mikey@neuling.org> Acked-by: Stewart Smith <stewart@linux.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
2018-06-24 18:34:55 -07:00
DAWR issues on POWER9
docs: powerpc: convert docs to ReST and rename to *.rst Convert docs to ReST and add them to the arch-specific book. The conversion here was trivial, as almost every file there was already using an elegant format close to ReST standard. The changes were mostly to mark literal blocks and add a few missing section title identifiers. One note with regards to "--": on Sphinx, this can't be used to identify a list, as it will format it badly. This can be used, however, to identify a long hyphen - and "---" is an even longer one. At its new index.rst, let's add a :orphan: while this is not linked to the main index.rst file, in order to avoid build warnings. Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Acked-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com> # cxl
2019-04-10 04:32:42 -07:00
=====================
powerpc: Document issues with the DAWR on POWER9 Signed-off-by: Michael Neuling <mikey@neuling.org> Acked-by: Stewart Smith <stewart@linux.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
2018-06-24 18:34:55 -07:00
powerpc: Enable the DAWR on POWER9 DD2.3 and above The hardware bug in POWER9 preventing use of the DAWR was fixed in DD2.3. Set the CPU_FTR_DAWR feature bit on these newer systems to start using it again, and update the documentation accordingly. The CPU features for DD2.3 are currently determined by "DD2.2 or later" logic. In adding DD2.3 as a discrete case for the first time here, I'm carrying the quirks of DD2.2 forward to keep all behavior outside of this DAWR change the same. This leaves the assessment and potential removal of those quirks on DD2.3 for later. Signed-off-by: Reza Arbab <arbab@linux.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20220503170152.23412-1-arbab@linux.ibm.com
2022-05-03 10:01:52 -07:00
On older POWER9 processors, the Data Address Watchpoint Register (DAWR) can
cause a checkstop if it points to cache inhibited (CI) memory. Currently Linux
has no way to distinguish CI memory when configuring the DAWR, so on affected
systems, the DAWR is disabled.
Affected processor revisions
============================
This issue is only present on processors prior to v2.3. The revision can be
found in /proc/cpuinfo::
processor : 0
cpu : POWER9, altivec supported
clock : 3800.000000MHz
revision : 2.3 (pvr 004e 1203)
On a system with the issue, the DAWR is disabled as detailed below.
powerpc: Document issues with the DAWR on POWER9 Signed-off-by: Michael Neuling <mikey@neuling.org> Acked-by: Stewart Smith <stewart@linux.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
2018-06-24 18:34:55 -07:00
Technical Details:
docs: powerpc: convert docs to ReST and rename to *.rst Convert docs to ReST and add them to the arch-specific book. The conversion here was trivial, as almost every file there was already using an elegant format close to ReST standard. The changes were mostly to mark literal blocks and add a few missing section title identifiers. One note with regards to "--": on Sphinx, this can't be used to identify a list, as it will format it badly. This can be used, however, to identify a long hyphen - and "---" is an even longer one. At its new index.rst, let's add a :orphan: while this is not linked to the main index.rst file, in order to avoid build warnings. Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Acked-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com> # cxl
2019-04-10 04:32:42 -07:00
==================
powerpc: Document issues with the DAWR on POWER9 Signed-off-by: Michael Neuling <mikey@neuling.org> Acked-by: Stewart Smith <stewart@linux.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
2018-06-24 18:34:55 -07:00
DAWR has 6 different ways of being set.
1) ptrace
2) h_set_mode(DAWR)
3) h_set_dabr()
4) kvmppc_set_one_reg()
5) xmon
For ptrace, we now advertise zero breakpoints on POWER9 via the
PPC_PTRACE_GETHWDBGINFO call. This results in GDB falling back to
software emulation of the watchpoint (which is slow).
h_set_mode(DAWR) and h_set_dabr() will now return an error to the
guest on a POWER9 host. Current Linux guests ignore this error, so
they will silently not get the DAWR.
kvmppc_set_one_reg() will store the value in the vcpu but won't
actually set it on POWER9 hardware. This is done so we don't break
migration from POWER8 to POWER9, at the cost of silently losing the
DAWR on the migration.
For xmon, the 'bd' command will return an error on P9.
Consequences for users
docs: powerpc: convert docs to ReST and rename to *.rst Convert docs to ReST and add them to the arch-specific book. The conversion here was trivial, as almost every file there was already using an elegant format close to ReST standard. The changes were mostly to mark literal blocks and add a few missing section title identifiers. One note with regards to "--": on Sphinx, this can't be used to identify a list, as it will format it badly. This can be used, however, to identify a long hyphen - and "---" is an even longer one. At its new index.rst, let's add a :orphan: while this is not linked to the main index.rst file, in order to avoid build warnings. Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Acked-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com> # cxl
2019-04-10 04:32:42 -07:00
======================
powerpc: Document issues with the DAWR on POWER9 Signed-off-by: Michael Neuling <mikey@neuling.org> Acked-by: Stewart Smith <stewart@linux.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
2018-06-24 18:34:55 -07:00
For GDB watchpoints (ie 'watch' command) on POWER9 bare metal , GDB
will accept the command. Unfortunately since there is no hardware
support for the watchpoint, GDB will software emulate the watchpoint
making it run very slowly.
The same will also be true for any guests started on a POWER9
host. The watchpoint will fail and GDB will fall back to software
emulation.
If a guest is started on a POWER8 host, GDB will accept the watchpoint
and configure the hardware to use the DAWR. This will run at full
speed since it can use the hardware emulation. Unfortunately if this
guest is migrated to a POWER9 host, the watchpoint will be lost on the
POWER9. Loads and stores to the watchpoint locations will not be
trapped in GDB. The watchpoint is remembered, so if the guest is
migrated back to the POWER8 host, it will start working again.
powerpc: Add force enable of DAWR on P9 option This adds a flag so that the DAWR can be enabled on P9 via: echo Y > /sys/kernel/debug/powerpc/dawr_enable_dangerous The DAWR was previously force disabled on POWER9 in: 9654153158 powerpc: Disable DAWR in the base POWER9 CPU features Also see Documentation/powerpc/DAWR-POWER9.txt This is a dangerous setting, USE AT YOUR OWN RISK. Some users may not care about a bad user crashing their box (ie. single user/desktop systems) and really want the DAWR. This allows them to force enable DAWR. This flag can also be used to disable DAWR access. Once this is cleared, all DAWR access should be cleared immediately and your machine once again safe from crashing. Userspace may get confused by toggling this. If DAWR is force enabled/disabled between getting the number of breakpoints (via PTRACE_GETHWDBGINFO) and setting the breakpoint, userspace will get an inconsistent view of what's available. Similarly for guests. For the DAWR to be enabled in a KVM guest, the DAWR needs to be force enabled in the host AND the guest. For this reason, this won't work on POWERVM as it doesn't allow the HCALL to work. Writes of 'Y' to the dawr_enable_dangerous file will fail if the hypervisor doesn't support writing the DAWR. To double check the DAWR is working, run this kernel selftest: tools/testing/selftests/powerpc/ptrace/ptrace-hwbreak.c Any errors/failures/skips mean something is wrong. Signed-off-by: Michael Neuling <mikey@neuling.org> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
2019-03-31 23:03:12 -07:00
Force enabling the DAWR
docs: powerpc: convert docs to ReST and rename to *.rst Convert docs to ReST and add them to the arch-specific book. The conversion here was trivial, as almost every file there was already using an elegant format close to ReST standard. The changes were mostly to mark literal blocks and add a few missing section title identifiers. One note with regards to "--": on Sphinx, this can't be used to identify a list, as it will format it badly. This can be used, however, to identify a long hyphen - and "---" is an even longer one. At its new index.rst, let's add a :orphan: while this is not linked to the main index.rst file, in order to avoid build warnings. Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Acked-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com> # cxl
2019-04-10 04:32:42 -07:00
=======================
Kernels (since ~v5.2) have an option to force enable the DAWR via::
powerpc: Add force enable of DAWR on P9 option This adds a flag so that the DAWR can be enabled on P9 via: echo Y > /sys/kernel/debug/powerpc/dawr_enable_dangerous The DAWR was previously force disabled on POWER9 in: 9654153158 powerpc: Disable DAWR in the base POWER9 CPU features Also see Documentation/powerpc/DAWR-POWER9.txt This is a dangerous setting, USE AT YOUR OWN RISK. Some users may not care about a bad user crashing their box (ie. single user/desktop systems) and really want the DAWR. This allows them to force enable DAWR. This flag can also be used to disable DAWR access. Once this is cleared, all DAWR access should be cleared immediately and your machine once again safe from crashing. Userspace may get confused by toggling this. If DAWR is force enabled/disabled between getting the number of breakpoints (via PTRACE_GETHWDBGINFO) and setting the breakpoint, userspace will get an inconsistent view of what's available. Similarly for guests. For the DAWR to be enabled in a KVM guest, the DAWR needs to be force enabled in the host AND the guest. For this reason, this won't work on POWERVM as it doesn't allow the HCALL to work. Writes of 'Y' to the dawr_enable_dangerous file will fail if the hypervisor doesn't support writing the DAWR. To double check the DAWR is working, run this kernel selftest: tools/testing/selftests/powerpc/ptrace/ptrace-hwbreak.c Any errors/failures/skips mean something is wrong. Signed-off-by: Michael Neuling <mikey@neuling.org> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
2019-03-31 23:03:12 -07:00
echo Y > /sys/kernel/debug/powerpc/dawr_enable_dangerous
This enables the DAWR even on POWER9.
This is a dangerous setting, USE AT YOUR OWN RISK.
Some users may not care about a bad user crashing their box
(ie. single user/desktop systems) and really want the DAWR. This
allows them to force enable DAWR.
This flag can also be used to disable DAWR access. Once this is
cleared, all DAWR access should be cleared immediately and your
machine once again safe from crashing.
Userspace may get confused by toggling this. If DAWR is force
enabled/disabled between getting the number of breakpoints (via
PTRACE_GETHWDBGINFO) and setting the breakpoint, userspace will get an
inconsistent view of what's available. Similarly for guests.
For the DAWR to be enabled in a KVM guest, the DAWR needs to be force
enabled in the host AND the guest. For this reason, this won't work on
POWERVM as it doesn't allow the HCALL to work. Writes of 'Y' to the
dawr_enable_dangerous file will fail if the hypervisor doesn't support
writing the DAWR.
To double check the DAWR is working, run this kernel selftest:
docs: powerpc: convert docs to ReST and rename to *.rst Convert docs to ReST and add them to the arch-specific book. The conversion here was trivial, as almost every file there was already using an elegant format close to ReST standard. The changes were mostly to mark literal blocks and add a few missing section title identifiers. One note with regards to "--": on Sphinx, this can't be used to identify a list, as it will format it badly. This can be used, however, to identify a long hyphen - and "---" is an even longer one. At its new index.rst, let's add a :orphan: while this is not linked to the main index.rst file, in order to avoid build warnings. Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Acked-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com> # cxl
2019-04-10 04:32:42 -07:00
powerpc: Add force enable of DAWR on P9 option This adds a flag so that the DAWR can be enabled on P9 via: echo Y > /sys/kernel/debug/powerpc/dawr_enable_dangerous The DAWR was previously force disabled on POWER9 in: 9654153158 powerpc: Disable DAWR in the base POWER9 CPU features Also see Documentation/powerpc/DAWR-POWER9.txt This is a dangerous setting, USE AT YOUR OWN RISK. Some users may not care about a bad user crashing their box (ie. single user/desktop systems) and really want the DAWR. This allows them to force enable DAWR. This flag can also be used to disable DAWR access. Once this is cleared, all DAWR access should be cleared immediately and your machine once again safe from crashing. Userspace may get confused by toggling this. If DAWR is force enabled/disabled between getting the number of breakpoints (via PTRACE_GETHWDBGINFO) and setting the breakpoint, userspace will get an inconsistent view of what's available. Similarly for guests. For the DAWR to be enabled in a KVM guest, the DAWR needs to be force enabled in the host AND the guest. For this reason, this won't work on POWERVM as it doesn't allow the HCALL to work. Writes of 'Y' to the dawr_enable_dangerous file will fail if the hypervisor doesn't support writing the DAWR. To double check the DAWR is working, run this kernel selftest: tools/testing/selftests/powerpc/ptrace/ptrace-hwbreak.c Any errors/failures/skips mean something is wrong. Signed-off-by: Michael Neuling <mikey@neuling.org> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
2019-03-31 23:03:12 -07:00
tools/testing/selftests/powerpc/ptrace/ptrace-hwbreak.c
docs: powerpc: convert docs to ReST and rename to *.rst Convert docs to ReST and add them to the arch-specific book. The conversion here was trivial, as almost every file there was already using an elegant format close to ReST standard. The changes were mostly to mark literal blocks and add a few missing section title identifiers. One note with regards to "--": on Sphinx, this can't be used to identify a list, as it will format it badly. This can be used, however, to identify a long hyphen - and "---" is an even longer one. At its new index.rst, let's add a :orphan: while this is not linked to the main index.rst file, in order to avoid build warnings. Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Acked-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com> # cxl
2019-04-10 04:32:42 -07:00
powerpc: Add force enable of DAWR on P9 option This adds a flag so that the DAWR can be enabled on P9 via: echo Y > /sys/kernel/debug/powerpc/dawr_enable_dangerous The DAWR was previously force disabled on POWER9 in: 9654153158 powerpc: Disable DAWR in the base POWER9 CPU features Also see Documentation/powerpc/DAWR-POWER9.txt This is a dangerous setting, USE AT YOUR OWN RISK. Some users may not care about a bad user crashing their box (ie. single user/desktop systems) and really want the DAWR. This allows them to force enable DAWR. This flag can also be used to disable DAWR access. Once this is cleared, all DAWR access should be cleared immediately and your machine once again safe from crashing. Userspace may get confused by toggling this. If DAWR is force enabled/disabled between getting the number of breakpoints (via PTRACE_GETHWDBGINFO) and setting the breakpoint, userspace will get an inconsistent view of what's available. Similarly for guests. For the DAWR to be enabled in a KVM guest, the DAWR needs to be force enabled in the host AND the guest. For this reason, this won't work on POWERVM as it doesn't allow the HCALL to work. Writes of 'Y' to the dawr_enable_dangerous file will fail if the hypervisor doesn't support writing the DAWR. To double check the DAWR is working, run this kernel selftest: tools/testing/selftests/powerpc/ptrace/ptrace-hwbreak.c Any errors/failures/skips mean something is wrong. Signed-off-by: Michael Neuling <mikey@neuling.org> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
2019-03-31 23:03:12 -07:00
Any errors/failures/skips mean something is wrong.
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