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target/riscv: Reduce overhead of MSTATUS_SUM change

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Kernel needs to access user mode memory e.g. during syscalls, the window
is usually opened up for a very limited time through MSTATUS.SUM, the
overhead is too much if tlb_flush() gets called for every SUM change.

This patch creates a separate MMU index for S+SUM, so that it's not
necessary to flush tlb anymore when SUM changes. This is similar to how
ARM handles Privileged Access Never (PAN).

Result of 'pipe 10' from unixbench boosts from 223656 to 1705006. Many
other syscalls benefit a lot from this too.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Fei Wu <fei2.wu@intel.com>
Message-Id: <20230324054154.414846-3-fei2.wu@intel.com>
Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Weiwei Li <liweiwei@iscas.ac.cn>
Tested-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-Id: <20230325105429.1142530-8-richard.henderson@linaro.org>
Message-Id: <20230412114333.118895-8-richard.henderson@linaro.org>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
This commit is contained in:
Fei Wu 2023-04-12 13:43:15 +02:00 • committed by Alistair Francis
parent 47debc7280
commit c8f8a9957e
6 changed files with 35 additions and 10 deletions
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2
target/riscv/cpu.h
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@ -629,8 +629,6 @@ G_NORETURN void riscv_raise_exception(CPURISCVState *env,
target_ulong riscv_cpu_get_fflags(CPURISCVState *env);
void riscv_cpu_set_fflags(CPURISCVState *env, target_ulong);
#define TB_FLAGS_PRIV_HYP_ACCESS_MASK (1 << 2)
#include "exec/cpu-all.h"
FIELD(TB_FLAGS, MEM_IDX, 0, 3)