Current implementation of update_mmu_cache function performs local TLB
flush. It does not take into account ASID information. Besides, it does
not take into account other harts currently running the same mm context
or possible migration of the running context to other harts. Meanwhile
TLB flush is not performed for every context switch if ASID support
is enabled.
Patch [1] proposed to add ASID support to update_mmu_cache to avoid
flushing local TLB entirely. This patch takes into account other
harts currently running the same mm context as well as possible
migration of this context to other harts.
For this purpose the approach from flush_icache_mm is reused. Remote
harts currently running the same mm context are informed via SBI calls
that they need to flush their local TLBs. All the other harts are marked
as needing a deferred TLB flush when this mm context runs on them.
[1] https://lore.kernel.org/linux-riscv/20220821013926.8968-1-tjytimi@163.com/
Signed-off-by: Sergey Matyukevich <sergey.matyukevich@syntacore.com>
Fixes: 65d4b9c530 ("RISC-V: Implement ASID allocator")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/linux-riscv/20220829205219.283543-1-geomatsi@gmail.com/#t
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Currently, we do local TLB flush on every MM switch. This is very harsh on
performance because we are forcing page table walks after every MM switch.
This patch implements ASID allocator for assigning an ASID to a MM context.
The number of ASIDs are limited in HW so we create a logical entity named
CONTEXTID for assigning to MM context. The lower bits of CONTEXTID are ASID
and upper bits are VERSION number. The number of usable ASID bits supported
by HW are detected at boot-time by writing 1s to ASID bits in SATP CSR.
We allocate new CONTEXTID on first MM switch for a MM context where the
ASID is allocated from an ASID bitmap and VERSION is provide by an atomic
counter. At time of allocating new CONTEXTID, if we run out of available
ASIDs then:
1. We flush the ASID bitmap
2. Increment current VERSION atomic counter
3. Re-allocate ASID from ASID bitmap
4. Flush TLB on all CPUs
5. Try CONTEXTID re-assignment on all CPUs
Please note that we don't use ASID #0 because it is used at boot-time by
all CPUs for initial MM context. Also, newly created context is always
assigned CONTEXTID #0 (i.e. VERSION #0 and ASID #0) which is an invalid
context in our implementation.
Using above approach, we have virtually infinite CONTEXTIDs on-top-of
limited number of HW ASIDs. This approach is inspired from ASID allocator
used for Linux ARM/ARM64 but we have adapted it for RISC-V. Overall, this
ASID allocator helps us reduce rate of local TLB flushes on every CPU
thereby increasing performance.
This patch is tested on QEMU virt machine, Spike and SiFive Unleashed
board. On QEMU virt machine, we see some (3-5% approx) performance
improvement with SW emulated TLBs provided by QEMU. Unfortunately,
the ASID bits of the SATP CSR are not implemented on Spike and SiFive
Unleashed board so we don't see any change in performance. On real HW
having all ASID bits implemented, the performance gains will be much
more due improved sharing of TLB among different processes.
Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Palmer Dabbelt <palmerdabbelt@google.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
The kernel runs in M-mode without using page tables, and thus can't run
bare metal without help from additional firmware.
Most of the patch is just stubbing out code not needed without page
tables, but there is an interesting detail in the signals implementation:
- The normal RISC-V syscall ABI only implements rt_sigreturn as VDSO
entry point, but the ELF VDSO is not supported for nommu Linux.
We instead copy the code to call the syscall onto the stack.
In addition to enabling the nommu code a new defconfig for a small
kernel image that can run in nommu mode on qemu is also provided, to run
a kernel in qemu you can use the following command line:
qemu-system-riscv64 -smp 2 -m 64 -machine virt -nographic \
-kernel arch/riscv/boot/loader \
-drive file=rootfs.ext2,format=raw,id=hd0 \
-device virtio-blk-device,drive=hd0
Contains contributions from Damien Le Moal <Damien.LeMoal@wdc.com>.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Anup Patel <anup@brainfault.org>
[paul.walmsley@sifive.com: updated to apply; add CONFIG_MMU guards
around PCI_IOBASE definition to fix build issues; fixed checkpatch
issues; move the PCI_IO_* and VMEMMAP address space macros along
with the others; resolve sparse warning]
Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>
Based on 1 normalized pattern(s):
this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license as published by
the free software foundation version 2 this program is distributed
in the hope that it will be useful but without any warranty without
even the implied warranty of merchantability or fitness for a
particular purpose see the gnu general public license for more
details
extracted by the scancode license scanner the SPDX license identifier
GPL-2.0-only
has been chosen to replace the boilerplate/reference in 97 file(s).
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Allison Randal <allison@lohutok.net>
Reviewed-by: Alexios Zavras <alexios.zavras@intel.com>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190529141901.025053186@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
The RISC-V ISA allows for instruction caches that are not coherent WRT
stores, even on a single hart. As a result, we need to explicitly flush
the instruction cache whenever marking a dirty page as executable in
order to preserve the correct system behavior.
Local instruction caches aren't that scary (our implementations actually
flush the cache, but RISC-V is defined to allow higher-performance
implementations to exist), but RISC-V defines no way to perform an
instruction cache shootdown. When explicitly asked to do so we can
shoot down remote instruction caches via an IPI, but this is a bit on
the slow side.
Instead of requiring an IPI to all harts whenever marking a page as
executable, we simply flush the currently running harts. In order to
maintain correct behavior, we additionally mark every other hart as
needing a deferred instruction cache which will be taken before anything
runs on it.
Signed-off-by: Andrew Waterman <andrew@sifive.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
This patch contains code that is in some way visible to the user:
including via system calls, the VDSO, module loading and signal
handling. It also contains some generic code that is ABI visible.
Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>
