[PATCH v5 0/2] target/riscv: reduce MSTATUS_SUM overhead

[PATCH v5 0/2] target/riscv: reduce MSTATUS_SUM overhead

[Fei Wu]

v4 -> v5:
* add priv to tb_flags

v3 -> v4:
* seperate priv from mmu_idx
* use index 2 for S+SUM mmu_idx
* no tlb_flush for MPRV / MPP changes


Fei Wu (2):
  target/riscv: separate priv from mmu_idx
  target/riscv: reduce overhead of MSTATUS_SUM change

 target/riscv/cpu.h                            |  3 +--
 target/riscv/cpu_helper.c                     | 21 ++++++++++++++++---
 target/riscv/csr.c                            |  3 +--
 .../riscv/insn_trans/trans_privileged.c.inc   |  2 +-
 target/riscv/insn_trans/trans_rvh.c.inc       |  4 ++--
 target/riscv/insn_trans/trans_xthead.c.inc    |  7 +------
 target/riscv/internals.h                      | 14 +++++++++++++
 target/riscv/op_helper.c                      |  5 +++--
 target/riscv/translate.c                      |  3 +++
 9 files changed, 44 insertions(+), 18 deletions(-)

-- 
2.25.1

[PATCH v5 1/2] target/riscv: separate priv from mmu_idx

[Fei Wu]

Currently it's assumed the 2 low bits of mmu_idx map to privilege mode,
this assumption won't last as we are about to add more mmu_idx. Here an
individual priv field is added into TB_FLAGS.

Signed-off-by: Fei Wu <fei2.wu@intel.com>
---
 target/riscv/cpu.h                             | 2 +-
 target/riscv/cpu_helper.c                      | 4 +++-
 target/riscv/insn_trans/trans_privileged.c.inc | 2 +-
 target/riscv/insn_trans/trans_xthead.c.inc     | 7 +------
 target/riscv/translate.c                       | 3 +++
 5 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index 638e47c75a..ac3eb9abca 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -623,7 +623,6 @@ 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_MMU_MASK                3
 #define TB_FLAGS_PRIV_HYP_ACCESS_MASK   (1 << 2)
 #define TB_FLAGS_MSTATUS_FS MSTATUS_FS
 #define TB_FLAGS_MSTATUS_VS MSTATUS_VS
@@ -650,6 +649,7 @@ FIELD(TB_FLAGS, VTA, 24, 1)
 FIELD(TB_FLAGS, VMA, 25, 1)
 /* Native debug itrigger */
 FIELD(TB_FLAGS, ITRIGGER, 26, 1)
+FIELD(TB_FLAGS, PRIV, 27, 2)
 
 #ifdef TARGET_RISCV32
 #define riscv_cpu_mxl(env)  ((void)(env), MXL_RV32)
diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
index f88c503cf4..4e275b904a 100644
--- a/target/riscv/cpu_helper.c
+++ b/target/riscv/cpu_helper.c
@@ -82,6 +82,8 @@ void cpu_get_tb_cpu_state(CPURISCVState *env, target_ulong *pc,
     flags |= TB_FLAGS_MSTATUS_FS;
     flags |= TB_FLAGS_MSTATUS_VS;
 #else
+    flags = FIELD_DP32(flags, TB_FLAGS, PRIV, env->priv);
+
     flags |= cpu_mmu_index(env, 0);
     if (riscv_cpu_fp_enabled(env)) {
         flags |= env->mstatus & MSTATUS_FS;
@@ -762,7 +764,7 @@ static int get_physical_address(CPURISCVState *env, hwaddr *physical,
      * (riscv_cpu_do_interrupt) is correct */
     MemTxResult res;
     MemTxAttrs attrs = MEMTXATTRS_UNSPECIFIED;
-    int mode = mmu_idx & TB_FLAGS_PRIV_MMU_MASK;
+    int mode = env->priv;
     bool use_background = false;
     hwaddr ppn;
     RISCVCPU *cpu = env_archcpu(env);
diff --git a/target/riscv/insn_trans/trans_privileged.c.inc b/target/riscv/insn_trans/trans_privileged.c.inc
index 59501b2780..9305b18299 100644
--- a/target/riscv/insn_trans/trans_privileged.c.inc
+++ b/target/riscv/insn_trans/trans_privileged.c.inc
@@ -52,7 +52,7 @@ static bool trans_ebreak(DisasContext *ctx, arg_ebreak *a)
      * that no exception will be raised when fetching them.
      */
 
-    if (semihosting_enabled(ctx->mem_idx < PRV_S) &&
+    if (semihosting_enabled(ctx->priv < PRV_S) &&
         (pre_addr & TARGET_PAGE_MASK) == (post_addr & TARGET_PAGE_MASK)) {
         pre    = opcode_at(&ctx->base, pre_addr);
         ebreak = opcode_at(&ctx->base, ebreak_addr);
diff --git a/target/riscv/insn_trans/trans_xthead.c.inc b/target/riscv/insn_trans/trans_xthead.c.inc
index df504c3f2c..adfb53cb4c 100644
--- a/target/riscv/insn_trans/trans_xthead.c.inc
+++ b/target/riscv/insn_trans/trans_xthead.c.inc
@@ -265,12 +265,7 @@ static bool trans_th_tst(DisasContext *ctx, arg_th_tst *a)
 
 static inline int priv_level(DisasContext *ctx)
 {
-#ifdef CONFIG_USER_ONLY
-    return PRV_U;
-#else
-     /* Priv level is part of mem_idx. */
-    return ctx->mem_idx & TB_FLAGS_PRIV_MMU_MASK;
-#endif
+    return ctx->priv;
 }
 
 /* Test if priv level is M, S, or U (cannot fail). */
diff --git a/target/riscv/translate.c b/target/riscv/translate.c
index 0ee8ee147d..b215d18250 100644
--- a/target/riscv/translate.c
+++ b/target/riscv/translate.c
@@ -69,6 +69,7 @@ typedef struct DisasContext {
     uint32_t mstatus_hs_fs;
     uint32_t mstatus_hs_vs;
     uint32_t mem_idx;
+    uint32_t priv;
     /* Remember the rounding mode encoded in the previous fp instruction,
        which we have already installed into env->fp_status.  Or -1 for
        no previous fp instruction.  Note that we exit the TB when writing
@@ -1162,8 +1163,10 @@ static void riscv_tr_init_disas_context(DisasContextBase *dcbase, CPUState *cs)
     } else {
         ctx->virt_enabled = false;
     }
+    ctx->priv = FIELD_EX32(tb_flags, TB_FLAGS, PRIV);
 #else
     ctx->virt_enabled = false;
+    ctx->priv = PRV_U;
 #endif
     ctx->misa_ext = env->misa_ext;
     ctx->frm = -1;  /* unknown rounding mode */
-- 
2.25.1

Re: [PATCH v5 1/2] target/riscv: separate priv from mmu_idx

[Richard Henderson]

On 3/23/23 22:41, Fei Wu wrote:
> @@ -762,7 +764,7 @@ static int get_physical_address(CPURISCVState *env, hwaddr *physical,
>        * (riscv_cpu_do_interrupt) is correct */
>       MemTxResult res;
>       MemTxAttrs attrs = MEMTXATTRS_UNSPECIFIED;
> -    int mode = mmu_idx & TB_FLAGS_PRIV_MMU_MASK;
> +    int mode = env->priv;

This is not ok.

Or rather, it's ok as an intermediate step before fixing the other mis-uses of the 
interface in get_physical_address.

The interface to be provided by TCGCPUOps.tlb_fill is that (modulo tlb flushes) mmu_idx 
details the state we want the access to have.  We describe that state with the comment you 
move in patch 2:

+/*
+ * The current MMU Modes are:
+ *  - U                 0b000
+ *  - S                 0b001
+ *  - S+SUM             0b010
+ *  - M                 0b011
+ *  - HLV/HLVX/HSV adds 0b100
+ */

Anything that's in those bits shouldn't be re-examined from env.

So, in the short-term I'll give you

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

But for the long-term, let's see if we can untangle the ugly mess. I'll collect my 
thoughts and post some patches for discussion -- I think that will be clearer than the 
prose I began to write here.


r~

[PATCH v5 2/2] target/riscv: reduce overhead of MSTATUS_SUM change

[Fei Wu]

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.

Signed-off-by: Fei Wu <fei2.wu@intel.com>
---
 target/riscv/cpu.h                      |  1 -
 target/riscv/cpu_helper.c               | 17 +++++++++++++++--
 target/riscv/csr.c                      |  3 +--
 target/riscv/insn_trans/trans_rvh.c.inc |  4 ++--
 target/riscv/internals.h                | 14 ++++++++++++++
 target/riscv/op_helper.c                |  5 +++--
 6 files changed, 35 insertions(+), 9 deletions(-)

diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index ac3eb9abca..09d3b0a083 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -623,7 +623,6 @@ 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)
 #define TB_FLAGS_MSTATUS_FS MSTATUS_FS
 #define TB_FLAGS_MSTATUS_VS MSTATUS_VS
 
diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
index 4e275b904a..4a6097f133 100644
--- a/target/riscv/cpu_helper.c
+++ b/target/riscv/cpu_helper.c
@@ -21,6 +21,7 @@
 #include "qemu/log.h"
 #include "qemu/main-loop.h"
 #include "cpu.h"
+#include "internals.h"
 #include "pmu.h"
 #include "exec/exec-all.h"
 #include "instmap.h"
@@ -36,7 +37,19 @@ int riscv_cpu_mmu_index(CPURISCVState *env, bool ifetch)
 #ifdef CONFIG_USER_ONLY
     return 0;
 #else
-    return env->priv;
+    if (ifetch) {
+        return env->priv;
+    }
+
+    /* All priv -> mmu_idx mapping are here */
+    int mode = env->priv;
+    if (mode == PRV_M && get_field(env->mstatus, MSTATUS_MPRV)) {
+        mode = get_field(env->mstatus, MSTATUS_MPP);
+    }
+    if (mode == PRV_S && get_field(env->mstatus, MSTATUS_SUM)) {
+        return MMUIdx_S_SUM;
+    }
+    return mode;
 #endif
 }
 
@@ -598,7 +611,7 @@ void riscv_cpu_set_virt_enabled(CPURISCVState *env, bool enable)
 
 bool riscv_cpu_two_stage_lookup(int mmu_idx)
 {
-    return mmu_idx & TB_FLAGS_PRIV_HYP_ACCESS_MASK;
+    return mmu_idx & MMU_HYP_ACCESS_BIT;
 }
 
 int riscv_cpu_claim_interrupts(RISCVCPU *cpu, uint64_t interrupts)
diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index d522efc0b6..f74e40e66d 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -1246,8 +1246,7 @@ static RISCVException write_mstatus(CPURISCVState *env, int csrno,
     RISCVMXL xl = riscv_cpu_mxl(env);
 
     /* flush tlb on mstatus fields that affect VM */
-    if ((val ^ mstatus) & (MSTATUS_MXR | MSTATUS_MPP | MSTATUS_MPV |
-            MSTATUS_MPRV | MSTATUS_SUM)) {
+    if ((val ^ mstatus) & (MSTATUS_MXR | MSTATUS_MPV)) {
         tlb_flush(env_cpu(env));
     }
     mask = MSTATUS_SIE | MSTATUS_SPIE | MSTATUS_MIE | MSTATUS_MPIE |
diff --git a/target/riscv/insn_trans/trans_rvh.c.inc b/target/riscv/insn_trans/trans_rvh.c.inc
index 9248b48c36..15842f4282 100644
--- a/target/riscv/insn_trans/trans_rvh.c.inc
+++ b/target/riscv/insn_trans/trans_rvh.c.inc
@@ -40,7 +40,7 @@ static bool do_hlv(DisasContext *ctx, arg_r2 *a, MemOp mop)
     if (check_access(ctx)) {
         TCGv dest = dest_gpr(ctx, a->rd);
         TCGv addr = get_gpr(ctx, a->rs1, EXT_NONE);
-        int mem_idx = ctx->mem_idx | TB_FLAGS_PRIV_HYP_ACCESS_MASK;
+        int mem_idx = ctx->mem_idx | MMU_HYP_ACCESS_BIT;
         tcg_gen_qemu_ld_tl(dest, addr, mem_idx, mop);
         gen_set_gpr(ctx, a->rd, dest);
     }
@@ -87,7 +87,7 @@ static bool do_hsv(DisasContext *ctx, arg_r2_s *a, MemOp mop)
     if (check_access(ctx)) {
         TCGv addr = get_gpr(ctx, a->rs1, EXT_NONE);
         TCGv data = get_gpr(ctx, a->rs2, EXT_NONE);
-        int mem_idx = ctx->mem_idx | TB_FLAGS_PRIV_HYP_ACCESS_MASK;
+        int mem_idx = ctx->mem_idx | MMU_HYP_ACCESS_BIT;
         tcg_gen_qemu_st_tl(data, addr, mem_idx, mop);
     }
     return true;
diff --git a/target/riscv/internals.h b/target/riscv/internals.h
index 5620fbffb6..b55152a7dc 100644
--- a/target/riscv/internals.h
+++ b/target/riscv/internals.h
@@ -21,6 +21,20 @@
 
 #include "hw/registerfields.h"
 
+/*
+ * The current MMU Modes are:
+ *  - U                 0b000
+ *  - S                 0b001
+ *  - S+SUM             0b010
+ *  - M                 0b011
+ *  - HLV/HLVX/HSV adds 0b100
+ */
+#define MMUIdx_U            0
+#define MMUIdx_S            1
+#define MMUIdx_S_SUM        2
+#define MMUIdx_M            3
+#define MMU_HYP_ACCESS_BIT  (1 << 2)
+
 /* share data between vector helpers and decode code */
 FIELD(VDATA, VM, 0, 1)
 FIELD(VDATA, LMUL, 1, 3)
diff --git a/target/riscv/op_helper.c b/target/riscv/op_helper.c
index 84ee018f7d..962a061228 100644
--- a/target/riscv/op_helper.c
+++ b/target/riscv/op_helper.c
@@ -20,6 +20,7 @@
 
 #include "qemu/osdep.h"
 #include "cpu.h"
+#include "internals.h"
 #include "qemu/main-loop.h"
 #include "exec/exec-all.h"
 #include "exec/helper-proto.h"
@@ -428,14 +429,14 @@ void helper_hyp_gvma_tlb_flush(CPURISCVState *env)
 
 target_ulong helper_hyp_hlvx_hu(CPURISCVState *env, target_ulong address)
 {
-    int mmu_idx = cpu_mmu_index(env, true) | TB_FLAGS_PRIV_HYP_ACCESS_MASK;
+    int mmu_idx = cpu_mmu_index(env, true) | MMU_HYP_ACCESS_BIT;
 
     return cpu_lduw_mmuidx_ra(env, address, mmu_idx, GETPC());
 }
 
 target_ulong helper_hyp_hlvx_wu(CPURISCVState *env, target_ulong address)
 {
-    int mmu_idx = cpu_mmu_index(env, true) | TB_FLAGS_PRIV_HYP_ACCESS_MASK;
+    int mmu_idx = cpu_mmu_index(env, true) | MMU_HYP_ACCESS_BIT;
 
     return cpu_ldl_mmuidx_ra(env, address, mmu_idx, GETPC());
 }
-- 
2.25.1