This patch introduces a new Kconfig option which, when enabled, causes
the kernel to write the PID of the current task into the PROCID field
of the CONTEXTIDR on context switch. This is useful when analysing
hardware trace, since writes to this register can be configured to emit
an event into the trace stream.

The thread notifier for writing the PID is deliberately kept separate
from the ASID-writing code so that we can support newer processors using
LPAE, where the ASID is stored in TTBR0. As such, the switch_mm code is
updated to perform a read-modify-write sequence to ensure that we don't
clobber the PID on CPUs using the classic 2-level page tables.
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

Since the ASIDs must be unique to an mm across all the CPUs in a system,
the __new_context() function needs to broadcast a context reset event to
all the CPUs during ASID allocation if a roll-over occurred. Such IPIs
cannot be issued with interrupts disabled and ARM had to define
__ARCH_WANT_INTERRUPTS_ON_CTXSW.

This patch changes the check_context() function to
check_and_switch_context() called from switch_mm(). In case of
ASID-capable CPUs (ARMv6 onwards), if a new ASID is needed and the
interrupts are disabled, it defers the __new_context() and
cpu_switch_mm() calls to the post-lock switch hook where the interrupts
are enabled. Setting the reserved TTBR0 was also moved to
check_and_switch_context() from cpu_v7_switch_mm().
Reviewed-by: NWill Deacon <will.deacon@arm.com>
Tested-by: NWill Deacon <will.deacon@arm.com>
Reviewed-by: NFrank Rowand <frank.rowand@am.sony.com>
Tested-by: NMarc Zyngier <Marc.Zyngier@arm.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

On ARMv7 CPUs that cache first level page table entries (like the
Cortex-A15), using a reserved ASID while changing the TTBR or flushing
the TLB is unsafe.

This is because the CPU may cache the first level entry as the result of
a speculative memory access while the reserved ASID is assigned. After
the process owning the page tables dies, the memory will be reallocated
and may be written with junk values which can be interpreted as global,
valid PTEs by the processor. This will result in the TLB being populated
with bogus global entries.

This patch avoids the use of a reserved context ID in the v7 switch_mm
and ASID rollover code by temporarily using the swapper_pg_dir pointed
at by TTBR1, which contains only global entries that are not tagged
with ASIDs.
Reviewed-by: NFrank Rowand <frank.rowand@am.sony.com>
Tested-by: NMarc Zyngier <Marc.Zyngier@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
[catalin.marinas@arm.com: add LPAE support]
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

This patch modifies the proc-v7.S file so that it only contains code
shared between classic MMU and LPAE. The non-common code is factored out
into a separate file.
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>