[PATCH v2] target: riscv: Add Svvptc extension support

[PATCH v2] target: riscv: Add Svvptc extension support

[Alexandre Ghiti]

The Svvptc extension describes a uarch that does not cache invalid TLB
entries: that's the case for qemu so there is nothing particular to
implement other than the introduction of this extension.

Since qemu already exposes Svvptc behaviour, let's enable it by default
since it allows to drastically reduce the number of sfence.vma emitted
by S-mode.

Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
---
Changes in v2:
- Rebase on top of master
- Enable Svvptc by default

 target/riscv/cpu.c     | 2 ++
 target/riscv/cpu_cfg.h | 1 +
 2 files changed, 3 insertions(+)

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index c53b0d5b40..19421c8a45 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -192,6 +192,7 @@ const RISCVIsaExtData isa_edata_arr[] = {
     ISA_EXT_DATA_ENTRY(svinval, PRIV_VERSION_1_12_0, ext_svinval),
     ISA_EXT_DATA_ENTRY(svnapot, PRIV_VERSION_1_12_0, ext_svnapot),
     ISA_EXT_DATA_ENTRY(svpbmt, PRIV_VERSION_1_12_0, ext_svpbmt),
+    ISA_EXT_DATA_ENTRY(svvptc, PRIV_VERSION_1_12_0, ext_svvptc),
     ISA_EXT_DATA_ENTRY(xtheadba, PRIV_VERSION_1_11_0, ext_xtheadba),
     ISA_EXT_DATA_ENTRY(xtheadbb, PRIV_VERSION_1_11_0, ext_xtheadbb),
     ISA_EXT_DATA_ENTRY(xtheadbs, PRIV_VERSION_1_11_0, ext_xtheadbs),
@@ -1499,6 +1500,7 @@ const RISCVCPUMultiExtConfig riscv_cpu_extensions[] = {
     MULTI_EXT_CFG_BOOL("svinval", ext_svinval, false),
     MULTI_EXT_CFG_BOOL("svnapot", ext_svnapot, false),
     MULTI_EXT_CFG_BOOL("svpbmt", ext_svpbmt, false),
+    MULTI_EXT_CFG_BOOL("svvptc", ext_svvptc, true),
 
     MULTI_EXT_CFG_BOOL("zicntr", ext_zicntr, true),
     MULTI_EXT_CFG_BOOL("zihpm", ext_zihpm, true),
diff --git a/target/riscv/cpu_cfg.h b/target/riscv/cpu_cfg.h
index fb7eebde52..62612ae348 100644
--- a/target/riscv/cpu_cfg.h
+++ b/target/riscv/cpu_cfg.h
@@ -78,6 +78,7 @@ struct RISCVCPUConfig {
     bool ext_svinval;
     bool ext_svnapot;
     bool ext_svpbmt;
+    bool ext_svvptc;
     bool ext_zdinx;
     bool ext_zaamo;
     bool ext_zacas;
-- 
2.39.2

Re: [PATCH v2] target: riscv: Add Svvptc extension support

[Andrew Jones]

On Thu, Jul 18, 2024 at 06:07:37PM GMT, Alexandre Ghiti wrote:
> The Svvptc extension describes a uarch that does not cache invalid TLB
> entries: that's the case for qemu so there is nothing particular to
> implement other than the introduction of this extension.
> 
> Since qemu already exposes Svvptc behaviour, let's enable it by default
> since it allows to drastically reduce the number of sfence.vma emitted
> by S-mode.
> 
> Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
> ---
> Changes in v2:
> - Rebase on top of master
> - Enable Svvptc by default
> 
>  target/riscv/cpu.c     | 2 ++
>  target/riscv/cpu_cfg.h | 1 +
>  2 files changed, 3 insertions(+)
> 
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index c53b0d5b40..19421c8a45 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -192,6 +192,7 @@ const RISCVIsaExtData isa_edata_arr[] = {
>      ISA_EXT_DATA_ENTRY(svinval, PRIV_VERSION_1_12_0, ext_svinval),
>      ISA_EXT_DATA_ENTRY(svnapot, PRIV_VERSION_1_12_0, ext_svnapot),
>      ISA_EXT_DATA_ENTRY(svpbmt, PRIV_VERSION_1_12_0, ext_svpbmt),
> +    ISA_EXT_DATA_ENTRY(svvptc, PRIV_VERSION_1_12_0, ext_svvptc),

Since Svvptc was just ratified then it isn't spec 1.12. We need another
patch adding later versions first (there is at least one [1]).

[1] https://lists.gnu.org/archive/html/qemu-riscv/2024-05/msg00045.html

This version field is annoying to keep accurate... Maybe we should
make it optional and only specify a version when there are wider
spread changes, such as envcfg bits, which need to be present too.

>      ISA_EXT_DATA_ENTRY(xtheadba, PRIV_VERSION_1_11_0, ext_xtheadba),
>      ISA_EXT_DATA_ENTRY(xtheadbb, PRIV_VERSION_1_11_0, ext_xtheadbb),
>      ISA_EXT_DATA_ENTRY(xtheadbs, PRIV_VERSION_1_11_0, ext_xtheadbs),
> @@ -1499,6 +1500,7 @@ const RISCVCPUMultiExtConfig riscv_cpu_extensions[] = {
>      MULTI_EXT_CFG_BOOL("svinval", ext_svinval, false),
>      MULTI_EXT_CFG_BOOL("svnapot", ext_svnapot, false),
>      MULTI_EXT_CFG_BOOL("svpbmt", ext_svpbmt, false),
> +    MULTI_EXT_CFG_BOOL("svvptc", ext_svvptc, true),
>  
>      MULTI_EXT_CFG_BOOL("zicntr", ext_zicntr, true),
>      MULTI_EXT_CFG_BOOL("zihpm", ext_zihpm, true),
> diff --git a/target/riscv/cpu_cfg.h b/target/riscv/cpu_cfg.h
> index fb7eebde52..62612ae348 100644
> --- a/target/riscv/cpu_cfg.h
> +++ b/target/riscv/cpu_cfg.h
> @@ -78,6 +78,7 @@ struct RISCVCPUConfig {
>      bool ext_svinval;
>      bool ext_svnapot;
>      bool ext_svpbmt;
> +    bool ext_svvptc;
>      bool ext_zdinx;
>      bool ext_zaamo;
>      bool ext_zacas;
> -- 
> 2.39.2
> 
>

Thanks,
drew