qemu-e2k/accel/tcg/tb-jmp-cache.h

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/*
* The per-CPU TranslationBlock jump cache.
*
* Copyright (c) 2003 Fabrice Bellard
*
* SPDX-License-Identifier: GPL-2.0-or-later
*/
#ifndef ACCEL_TCG_TB_JMP_CACHE_H
#define ACCEL_TCG_TB_JMP_CACHE_H
#define TB_JMP_CACHE_BITS 12
#define TB_JMP_CACHE_SIZE (1 << TB_JMP_CACHE_BITS)
/*
cpu-exec: simplify jump cache management Unless I'm missing something egregious, the jmp cache is only every populated with a valid entry by the same thread that reads the cache. Therefore, the contents of any valid entry are always consistent and there is no need for any acquire/release magic. Indeed ->tb has to be accessed with atomics, because concurrent invalidations would otherwise cause data races. But ->pc is only ever accessed by one thread, and accesses to ->tb and ->pc within tb_lookup can never race with another tb_lookup. While the TranslationBlock (especially the flags) could be modified by a concurrent invalidation, store-release and load-acquire operations on the cache entry would not add any additional ordering beyond what you get from performing the accesses within a single thread. Because of this, there is really nothing to win in splitting the CF_PCREL and !CF_PCREL paths. It is easier to just always use the ->pc field in the jump cache. I noticed this while working on splitting commit 8ed558ec0cb ("accel/tcg: Introduce TARGET_TB_PCREL", 2022-10-04) into multiple pieces, for the sake of finding a more fine-grained bisection result for https://gitlab.com/qemu-project/qemu/-/issues/2092. It does not (and does not intend to) fix that issue; therefore it may make sense to not commit it until the root cause of issue #2092 is found. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Tested-by: Alex Bennée <alex.bennee@linaro.org> Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Reviewed-by: Richard Henderson <richard.henderson@linaro.org> Message-Id: <20240122153409.351959-1-pbonzini@redhat.com> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2024-01-22 16:34:09 +01:00
* Invalidated in parallel; all accesses to 'tb' must be atomic.
* A valid entry is read/written by a single CPU, therefore there is
* no need for qatomic_rcu_read() and pc is always consistent with a
* non-NULL value of 'tb'. Strictly speaking pc is only needed for
* CF_PCREL, but it's used always for simplicity.
*/
struct CPUJumpCache {
cpu: free cpu->tb_jmp_cache with RCU Fixes the appended use-after-free. The root cause is that during tb invalidation we use CPU_FOREACH, and therefore to safely free a vCPU we must wait for an RCU grace period to elapse. $ x86_64-linux-user/qemu-x86_64 tests/tcg/x86_64-linux-user/munmap-pthread ================================================================= ==1800604==ERROR: AddressSanitizer: heap-use-after-free on address 0x62d0005f7418 at pc 0x5593da6704eb bp 0x7f4961a7ac70 sp 0x7f4961a7ac60 READ of size 8 at 0x62d0005f7418 thread T2 #0 0x5593da6704ea in tb_jmp_cache_inval_tb ../accel/tcg/tb-maint.c:244 #1 0x5593da6704ea in do_tb_phys_invalidate ../accel/tcg/tb-maint.c:290 #2 0x5593da670631 in tb_phys_invalidate__locked ../accel/tcg/tb-maint.c:306 #3 0x5593da670631 in tb_invalidate_phys_page_range__locked ../accel/tcg/tb-maint.c:542 #4 0x5593da67106d in tb_invalidate_phys_range ../accel/tcg/tb-maint.c:614 #5 0x5593da6a64d4 in target_munmap ../linux-user/mmap.c:766 #6 0x5593da6dba05 in do_syscall1 ../linux-user/syscall.c:10105 #7 0x5593da6f564c in do_syscall ../linux-user/syscall.c:13329 #8 0x5593da49e80c in cpu_loop ../linux-user/x86_64/../i386/cpu_loop.c:233 #9 0x5593da6be28c in clone_func ../linux-user/syscall.c:6633 #10 0x7f496231cb42 in start_thread nptl/pthread_create.c:442 #11 0x7f49623ae9ff (/lib/x86_64-linux-gnu/libc.so.6+0x1269ff) 0x62d0005f7418 is located 28696 bytes inside of 32768-byte region [0x62d0005f0400,0x62d0005f8400) freed by thread T148 here: #0 0x7f49627b6460 in __interceptor_free ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:52 #1 0x5593da5ac057 in cpu_exec_unrealizefn ../cpu.c:180 #2 0x5593da81f851 (/home/cota/src/qemu/build/qemu-x86_64+0x484851) Signed-off-by: Emilio Cota <cota@braap.org> Reviewed-by: Richard Henderson <richard.henderson@linaro.org> Message-Id: <20230111151628.320011-2-cota@braap.org> Signed-off-by: Alex Bennée <alex.bennee@linaro.org> Message-Id: <20230124180127.1881110-27-alex.bennee@linaro.org>
2023-01-24 19:01:18 +01:00
struct rcu_head rcu;
struct {
TranslationBlock *tb;
vaddr pc;
} array[TB_JMP_CACHE_SIZE];
};
#endif /* ACCEL_TCG_TB_JMP_CACHE_H */