[PATCH v2 0/3] Add Svadu Extension Support

[PATCH v2 0/3] Add Svadu Extension Support

[Yong-Xuan Wang]

Svadu is a RISC-V extension for hardware updating of PTE A/D bits. This
patch set adds support to enable Svadu extension for both host and guest
OS.

---
v2:
- add Co-developed-by: in PATCH1
- use riscv_has_extension_unlikely() to runtime patch the branch in PATCH1
- update dt-binding

Yong-Xuan Wang (3):
  RISC-V: Detect and Enable Svadu Extension Support
  dt-bindings: riscv: Add Svadu Entry
  RISC-V: KVM: Add Svadu Extension Support for Guest/VM

 Documentation/devicetree/bindings/riscv/extensions.yaml | 6 ++++++
 arch/riscv/include/asm/csr.h                            | 1 +
 arch/riscv/include/asm/hwcap.h                          | 1 +
 arch/riscv/include/asm/pgtable.h                        | 6 ++++++
 arch/riscv/include/uapi/asm/kvm.h                       | 1 +
 arch/riscv/kernel/cpufeature.c                          | 1 +
 arch/riscv/kvm/vcpu.c                                   | 3 +++
 arch/riscv/kvm/vcpu_onereg.c                            | 1 +
 8 files changed, 20 insertions(+)

-- 
2.17.1


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[PATCH v2 1/3] RISC-V: Detect and Enable Svadu Extension Support

[Yong-Xuan Wang]

We detect Svadu extension support from DTB and add arch_has_hw_pte_young()
to enable optimization in MGLRU and __wp_page_copy_user() if Svadu
extension is available.

Co-developed-by: Jinyu Tang <tjytimi@163.com>
Signed-off-by: Jinyu Tang <tjytimi@163.com>
Signed-off-by: Yong-Xuan Wang <yongxuan.wang@sifive.com>
---
 arch/riscv/include/asm/csr.h     | 1 +
 arch/riscv/include/asm/hwcap.h   | 1 +
 arch/riscv/include/asm/pgtable.h | 6 ++++++
 arch/riscv/kernel/cpufeature.c   | 1 +
 4 files changed, 9 insertions(+)

diff --git a/arch/riscv/include/asm/csr.h b/arch/riscv/include/asm/csr.h
index 777cb8299551..10648b372a2a 100644
--- a/arch/riscv/include/asm/csr.h
+++ b/arch/riscv/include/asm/csr.h
@@ -194,6 +194,7 @@
 /* xENVCFG flags */
 #define ENVCFG_STCE			(_AC(1, ULL) << 63)
 #define ENVCFG_PBMTE			(_AC(1, ULL) << 62)
+#define ENVCFG_HADE			(_AC(1, ULL) << 61)
 #define ENVCFG_CBZE			(_AC(1, UL) << 7)
 #define ENVCFG_CBCFE			(_AC(1, UL) << 6)
 #define ENVCFG_CBIE_SHIFT		4
diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
index b7b58258f6c7..1013661d6516 100644
--- a/arch/riscv/include/asm/hwcap.h
+++ b/arch/riscv/include/asm/hwcap.h
@@ -58,6 +58,7 @@
 #define RISCV_ISA_EXT_ZICSR		40
 #define RISCV_ISA_EXT_ZIFENCEI		41
 #define RISCV_ISA_EXT_ZIHPM		42
+#define RISCV_ISA_EXT_SVADU		43
 
 #define RISCV_ISA_EXT_MAX		64
 
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index b2ba3f79cfe9..028b700cd27b 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -629,6 +629,12 @@ static inline pgprot_t pgprot_writecombine(pgprot_t _prot)
 	return __pgprot(prot);
 }
 
+#define arch_has_hw_pte_young arch_has_hw_pte_young
+static inline bool arch_has_hw_pte_young(void)
+{
+	return riscv_has_extension_unlikely(RISCV_ISA_EXT_SVADU);
+}
+
 /*
  * THP functions
  */
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index 1cfbba65d11a..ead378c04991 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -178,6 +178,7 @@ const struct riscv_isa_ext_data riscv_isa_ext[] = {
 	__RISCV_ISA_EXT_DATA(ssaia, RISCV_ISA_EXT_SSAIA),
 	__RISCV_ISA_EXT_DATA(sscofpmf, RISCV_ISA_EXT_SSCOFPMF),
 	__RISCV_ISA_EXT_DATA(sstc, RISCV_ISA_EXT_SSTC),
+	__RISCV_ISA_EXT_DATA(svadu, RISCV_ISA_EXT_SVADU),
 	__RISCV_ISA_EXT_DATA(svinval, RISCV_ISA_EXT_SVINVAL),
 	__RISCV_ISA_EXT_DATA(svnapot, RISCV_ISA_EXT_SVNAPOT),
 	__RISCV_ISA_EXT_DATA(svpbmt, RISCV_ISA_EXT_SVPBMT),
-- 
2.17.1


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[PATCH v2 2/3] dt-bindings: riscv: Add Svadu Entry

[Yong-Xuan Wang]

Add an entry for the Svadu extension to the riscv,isa-extensions property.

Signed-off-by: Yong-Xuan Wang <yongxuan.wang@sifive.com>
---
 Documentation/devicetree/bindings/riscv/extensions.yaml | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/devicetree/bindings/riscv/extensions.yaml b/Documentation/devicetree/bindings/riscv/extensions.yaml
index cc1f546fdbdc..b5a0aed0165b 100644
--- a/Documentation/devicetree/bindings/riscv/extensions.yaml
+++ b/Documentation/devicetree/bindings/riscv/extensions.yaml
@@ -147,6 +147,12 @@ properties:
             ratified at commit 3f9ed34 ("Add ability to manually trigger
             workflow. (#2)") of riscv-time-compare.
 
+        - const: svadu
+          description: |
+            The standard Svadu supervisor-level extension for hardware updating
+            of PTE A/D bits as frozen at commit b65e07c ("move to Frozen
+            state") of riscv-svadu.
+
         - const: svinval
           description:
             The standard Svinval supervisor-level extension for fine-grained
-- 
2.17.1


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[PATCH v2 3/3] RISC-V: KVM: Add Svadu Extension Support for Guest/VM

[Yong-Xuan Wang]

We extend the KVM ISA extension ONE_REG interface to allow VMM
tools  to detect and enable Svadu extension for Guest/VM.

Also set the HADE bit in henvcfg CSR if Svadu extension is
available for Guest/VM.

Signed-off-by: Yong-Xuan Wang <yongxuan.wang@sifive.com>
---
 arch/riscv/include/uapi/asm/kvm.h | 1 +
 arch/riscv/kvm/vcpu.c             | 3 +++
 arch/riscv/kvm/vcpu_onereg.c      | 1 +
 3 files changed, 5 insertions(+)

diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
index 992c5e407104..3c7a6c762d0f 100644
--- a/arch/riscv/include/uapi/asm/kvm.h
+++ b/arch/riscv/include/uapi/asm/kvm.h
@@ -131,6 +131,7 @@ enum KVM_RISCV_ISA_EXT_ID {
 	KVM_RISCV_ISA_EXT_ZICSR,
 	KVM_RISCV_ISA_EXT_ZIFENCEI,
 	KVM_RISCV_ISA_EXT_ZIHPM,
+	KVM_RISCV_ISA_EXT_SVADU,
 	KVM_RISCV_ISA_EXT_MAX,
 };
 
diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
index 82229db1ce73..91b92a1f4e33 100644
--- a/arch/riscv/kvm/vcpu.c
+++ b/arch/riscv/kvm/vcpu.c
@@ -487,6 +487,9 @@ static void kvm_riscv_vcpu_update_config(const unsigned long *isa)
 	if (riscv_isa_extension_available(isa, ZICBOZ))
 		henvcfg |= ENVCFG_CBZE;
 
+	if (riscv_isa_extension_available(isa, SVADU))
+		henvcfg |= ENVCFG_HADE;
+
 	csr_write(CSR_HENVCFG, henvcfg);
 #ifdef CONFIG_32BIT
 	csr_write(CSR_HENVCFGH, henvcfg >> 32);
diff --git a/arch/riscv/kvm/vcpu_onereg.c b/arch/riscv/kvm/vcpu_onereg.c
index 1b7e9fa265cb..211915dad677 100644
--- a/arch/riscv/kvm/vcpu_onereg.c
+++ b/arch/riscv/kvm/vcpu_onereg.c
@@ -36,6 +36,7 @@ static const unsigned long kvm_isa_ext_arr[] = {
 	/* Multi letter extensions (alphabetically sorted) */
 	KVM_ISA_EXT_ARR(SSAIA),
 	KVM_ISA_EXT_ARR(SSTC),
+	KVM_ISA_EXT_ARR(SVADU),
 	KVM_ISA_EXT_ARR(SVINVAL),
 	KVM_ISA_EXT_ARR(SVNAPOT),
 	KVM_ISA_EXT_ARR(SVPBMT),
-- 
2.17.1


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Re: [PATCH v2 2/3] dt-bindings: riscv: Add Svadu Entry

[Conor Dooley]

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On Fri, Sep 22, 2023 at 08:56:48AM +0000, Yong-Xuan Wang wrote:
> Add an entry for the Svadu extension to the riscv,isa-extensions property.
> 
> Signed-off-by: Yong-Xuan Wang <yongxuan.wang@sifive.com>

Acked-by: Conor Dooley <conor.dooley@microchip.com>

Thanks,
Conor.

> ---
>  Documentation/devicetree/bindings/riscv/extensions.yaml | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/riscv/extensions.yaml b/Documentation/devicetree/bindings/riscv/extensions.yaml
> index cc1f546fdbdc..b5a0aed0165b 100644
> --- a/Documentation/devicetree/bindings/riscv/extensions.yaml
> +++ b/Documentation/devicetree/bindings/riscv/extensions.yaml
> @@ -147,6 +147,12 @@ properties:
>              ratified at commit 3f9ed34 ("Add ability to manually trigger
>              workflow. (#2)") of riscv-time-compare.
>  
> +        - const: svadu
> +          description: |
> +            The standard Svadu supervisor-level extension for hardware updating
> +            of PTE A/D bits as frozen at commit b65e07c ("move to Frozen
> +            state") of riscv-svadu.
> +
>          - const: svinval
>            description:
>              The standard Svinval supervisor-level extension for fine-grained
> -- 
> 2.17.1
> 

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Re: [PATCH v2 1/3] RISC-V: Detect and Enable Svadu Extension Support

[Conor Dooley]

[-- Attachment #1.1: Type: text/plain, Size: 477 bytes --]

On Fri, Sep 22, 2023 at 08:56:47AM +0000, Yong-Xuan Wang wrote:
> We detect Svadu extension support from DTB and add arch_has_hw_pte_young()
> to enable optimization in MGLRU and __wp_page_copy_user() if Svadu
> extension is available.
> 
> Co-developed-by: Jinyu Tang <tjytimi@163.com>
> Signed-off-by: Jinyu Tang <tjytimi@163.com>
> Signed-off-by: Yong-Xuan Wang <yongxuan.wang@sifive.com>

Reviewed-by: Conor Dooley <conor.dooley@microchip.com>

Thanks,
Conor.

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Re: [PATCH v2 1/3] RISC-V: Detect and Enable Svadu Extension Support

[Andrew Jones]

On Fri, Sep 22, 2023 at 08:56:47AM +0000, Yong-Xuan Wang wrote:
> We detect Svadu extension support from DTB and add arch_has_hw_pte_young()
> to enable optimization in MGLRU and __wp_page_copy_user() if Svadu
> extension is available.
> 
> Co-developed-by: Jinyu Tang <tjytimi@163.com>
> Signed-off-by: Jinyu Tang <tjytimi@163.com>
> Signed-off-by: Yong-Xuan Wang <yongxuan.wang@sifive.com>
> ---
>  arch/riscv/include/asm/csr.h     | 1 +
>  arch/riscv/include/asm/hwcap.h   | 1 +
>  arch/riscv/include/asm/pgtable.h | 6 ++++++
>  arch/riscv/kernel/cpufeature.c   | 1 +
>  4 files changed, 9 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/csr.h b/arch/riscv/include/asm/csr.h
> index 777cb8299551..10648b372a2a 100644
> --- a/arch/riscv/include/asm/csr.h
> +++ b/arch/riscv/include/asm/csr.h
> @@ -194,6 +194,7 @@
>  /* xENVCFG flags */
>  #define ENVCFG_STCE			(_AC(1, ULL) << 63)
>  #define ENVCFG_PBMTE			(_AC(1, ULL) << 62)
> +#define ENVCFG_HADE			(_AC(1, ULL) << 61)

This bit is named 'ADUE' in the spec. Why are we calling it HADE?

>  #define ENVCFG_CBZE			(_AC(1, UL) << 7)
>  #define ENVCFG_CBCFE			(_AC(1, UL) << 6)
>  #define ENVCFG_CBIE_SHIFT		4
> diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> index b7b58258f6c7..1013661d6516 100644
> --- a/arch/riscv/include/asm/hwcap.h
> +++ b/arch/riscv/include/asm/hwcap.h
> @@ -58,6 +58,7 @@
>  #define RISCV_ISA_EXT_ZICSR		40
>  #define RISCV_ISA_EXT_ZIFENCEI		41
>  #define RISCV_ISA_EXT_ZIHPM		42
> +#define RISCV_ISA_EXT_SVADU		43
>  
>  #define RISCV_ISA_EXT_MAX		64
>  
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index b2ba3f79cfe9..028b700cd27b 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -629,6 +629,12 @@ static inline pgprot_t pgprot_writecombine(pgprot_t _prot)
>  	return __pgprot(prot);
>  }
>  
> +#define arch_has_hw_pte_young arch_has_hw_pte_young
> +static inline bool arch_has_hw_pte_young(void)
> +{
> +	return riscv_has_extension_unlikely(RISCV_ISA_EXT_SVADU);
> +}
> +
>  /*
>   * THP functions
>   */
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 1cfbba65d11a..ead378c04991 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -178,6 +178,7 @@ const struct riscv_isa_ext_data riscv_isa_ext[] = {
>  	__RISCV_ISA_EXT_DATA(ssaia, RISCV_ISA_EXT_SSAIA),
>  	__RISCV_ISA_EXT_DATA(sscofpmf, RISCV_ISA_EXT_SSCOFPMF),
>  	__RISCV_ISA_EXT_DATA(sstc, RISCV_ISA_EXT_SSTC),
> +	__RISCV_ISA_EXT_DATA(svadu, RISCV_ISA_EXT_SVADU),
>  	__RISCV_ISA_EXT_DATA(svinval, RISCV_ISA_EXT_SVINVAL),
>  	__RISCV_ISA_EXT_DATA(svnapot, RISCV_ISA_EXT_SVNAPOT),
>  	__RISCV_ISA_EXT_DATA(svpbmt, RISCV_ISA_EXT_SVPBMT),
> -- 
> 2.17.1
>

Thanks,
drew

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Re: [PATCH v2 2/3] dt-bindings: riscv: Add Svadu Entry

[Andrew Jones]

On Fri, Sep 22, 2023 at 08:56:48AM +0000, Yong-Xuan Wang wrote:
> Add an entry for the Svadu extension to the riscv,isa-extensions property.
> 
> Signed-off-by: Yong-Xuan Wang <yongxuan.wang@sifive.com>
> ---
>  Documentation/devicetree/bindings/riscv/extensions.yaml | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/riscv/extensions.yaml b/Documentation/devicetree/bindings/riscv/extensions.yaml
> index cc1f546fdbdc..b5a0aed0165b 100644
> --- a/Documentation/devicetree/bindings/riscv/extensions.yaml
> +++ b/Documentation/devicetree/bindings/riscv/extensions.yaml
> @@ -147,6 +147,12 @@ properties:
>              ratified at commit 3f9ed34 ("Add ability to manually trigger
>              workflow. (#2)") of riscv-time-compare.
>  
> +        - const: svadu
> +          description: |
> +            The standard Svadu supervisor-level extension for hardware updating
> +            of PTE A/D bits as frozen at commit b65e07c ("move to Frozen
> +            state") of riscv-svadu.
> +
>          - const: svinval
>            description:
>              The standard Svinval supervisor-level extension for fine-grained
> -- 
> 2.17.1
>

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>

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Re: [PATCH v2 1/3] RISC-V: Detect and Enable Svadu Extension Support

[Matthew Wilcox]

On Fri, Sep 22, 2023 at 08:56:47AM +0000, Yong-Xuan Wang wrote:
> We detect Svadu extension support from DTB and add arch_has_hw_pte_young()
> to enable optimization in MGLRU and __wp_page_copy_user() if Svadu
> extension is available.

If you're going to cc people outside the RiscV space, you should probably
explain what Svadu is.  To me, it sounds like a Great Old One, maybe a
friend of Cthulhu?

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Re: [PATCH v2 3/3] RISC-V: KVM: Add Svadu Extension Support for Guest/VM

[Andrew Jones]

On Fri, Sep 22, 2023 at 08:56:49AM +0000, Yong-Xuan Wang wrote:
> We extend the KVM ISA extension ONE_REG interface to allow VMM
> tools  to detect and enable Svadu extension for Guest/VM.
> 
> Also set the HADE bit in henvcfg CSR if Svadu extension is
> available for Guest/VM.
> 
> Signed-off-by: Yong-Xuan Wang <yongxuan.wang@sifive.com>
> ---
>  arch/riscv/include/uapi/asm/kvm.h | 1 +
>  arch/riscv/kvm/vcpu.c             | 3 +++
>  arch/riscv/kvm/vcpu_onereg.c      | 1 +
>  3 files changed, 5 insertions(+)
> 
> diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
> index 992c5e407104..3c7a6c762d0f 100644
> --- a/arch/riscv/include/uapi/asm/kvm.h
> +++ b/arch/riscv/include/uapi/asm/kvm.h
> @@ -131,6 +131,7 @@ enum KVM_RISCV_ISA_EXT_ID {
>  	KVM_RISCV_ISA_EXT_ZICSR,
>  	KVM_RISCV_ISA_EXT_ZIFENCEI,
>  	KVM_RISCV_ISA_EXT_ZIHPM,
> +	KVM_RISCV_ISA_EXT_SVADU,

This register will show up as "new" in kselftests test[1]. We should add
another patch to this series to update the test to handle/test it.

[1] tools/testing/selftests/kvm/riscv/get-reg-list.c

>  	KVM_RISCV_ISA_EXT_MAX,
>  };
>  
> diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
> index 82229db1ce73..91b92a1f4e33 100644
> --- a/arch/riscv/kvm/vcpu.c
> +++ b/arch/riscv/kvm/vcpu.c
> @@ -487,6 +487,9 @@ static void kvm_riscv_vcpu_update_config(const unsigned long *isa)
>  	if (riscv_isa_extension_available(isa, ZICBOZ))
>  		henvcfg |= ENVCFG_CBZE;
>  
> +	if (riscv_isa_extension_available(isa, SVADU))
> +		henvcfg |= ENVCFG_HADE;
> +
>  	csr_write(CSR_HENVCFG, henvcfg);
>  #ifdef CONFIG_32BIT
>  	csr_write(CSR_HENVCFGH, henvcfg >> 32);
> diff --git a/arch/riscv/kvm/vcpu_onereg.c b/arch/riscv/kvm/vcpu_onereg.c
> index 1b7e9fa265cb..211915dad677 100644
> --- a/arch/riscv/kvm/vcpu_onereg.c
> +++ b/arch/riscv/kvm/vcpu_onereg.c
> @@ -36,6 +36,7 @@ static const unsigned long kvm_isa_ext_arr[] = {
>  	/* Multi letter extensions (alphabetically sorted) */
>  	KVM_ISA_EXT_ARR(SSAIA),
>  	KVM_ISA_EXT_ARR(SSTC),
> +	KVM_ISA_EXT_ARR(SVADU),
>  	KVM_ISA_EXT_ARR(SVINVAL),
>  	KVM_ISA_EXT_ARR(SVNAPOT),
>  	KVM_ISA_EXT_ARR(SVPBMT),
> -- 
> 2.17.1
>

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>

Thanks,
drew

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Re: [PATCH v2 1/3] RISC-V: Detect and Enable Svadu Extension Support

[Yong-Xuan Wang]

Hi drew,

On Wed, Sep 27, 2023 at 3:03 PM Andrew Jones <ajones@ventanamicro.com> wrote:
>
> On Fri, Sep 22, 2023 at 08:56:47AM +0000, Yong-Xuan Wang wrote:
> > We detect Svadu extension support from DTB and add arch_has_hw_pte_young()
> > to enable optimization in MGLRU and __wp_page_copy_user() if Svadu
> > extension is available.
> >
> > Co-developed-by: Jinyu Tang <tjytimi@163.com>
> > Signed-off-by: Jinyu Tang <tjytimi@163.com>
> > Signed-off-by: Yong-Xuan Wang <yongxuan.wang@sifive.com>
> > ---
> >  arch/riscv/include/asm/csr.h     | 1 +
> >  arch/riscv/include/asm/hwcap.h   | 1 +
> >  arch/riscv/include/asm/pgtable.h | 6 ++++++
> >  arch/riscv/kernel/cpufeature.c   | 1 +
> >  4 files changed, 9 insertions(+)
> >
> > diff --git a/arch/riscv/include/asm/csr.h b/arch/riscv/include/asm/csr.h
> > index 777cb8299551..10648b372a2a 100644
> > --- a/arch/riscv/include/asm/csr.h
> > +++ b/arch/riscv/include/asm/csr.h
> > @@ -194,6 +194,7 @@
> >  /* xENVCFG flags */
> >  #define ENVCFG_STCE                  (_AC(1, ULL) << 63)
> >  #define ENVCFG_PBMTE                 (_AC(1, ULL) << 62)
> > +#define ENVCFG_HADE                  (_AC(1, ULL) << 61)
>
> This bit is named 'ADUE' in the spec. Why are we calling it HADE?

This bit was called HADE in v0.1 spec. I will update it to ADUE in
patch v3. Thank you!

Regards,
Yong-Xuan


>
> >  #define ENVCFG_CBZE                  (_AC(1, UL) << 7)
> >  #define ENVCFG_CBCFE                 (_AC(1, UL) << 6)
> >  #define ENVCFG_CBIE_SHIFT            4
> > diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> > index b7b58258f6c7..1013661d6516 100644
> > --- a/arch/riscv/include/asm/hwcap.h
> > +++ b/arch/riscv/include/asm/hwcap.h
> > @@ -58,6 +58,7 @@
> >  #define RISCV_ISA_EXT_ZICSR          40
> >  #define RISCV_ISA_EXT_ZIFENCEI               41
> >  #define RISCV_ISA_EXT_ZIHPM          42
> > +#define RISCV_ISA_EXT_SVADU          43
> >
> >  #define RISCV_ISA_EXT_MAX            64
> >
> > diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> > index b2ba3f79cfe9..028b700cd27b 100644
> > --- a/arch/riscv/include/asm/pgtable.h
> > +++ b/arch/riscv/include/asm/pgtable.h
> > @@ -629,6 +629,12 @@ static inline pgprot_t pgprot_writecombine(pgprot_t _prot)
> >       return __pgprot(prot);
> >  }
> >
> > +#define arch_has_hw_pte_young arch_has_hw_pte_young
> > +static inline bool arch_has_hw_pte_young(void)
> > +{
> > +     return riscv_has_extension_unlikely(RISCV_ISA_EXT_SVADU);
> > +}
> > +
> >  /*
> >   * THP functions
> >   */
> > diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> > index 1cfbba65d11a..ead378c04991 100644
> > --- a/arch/riscv/kernel/cpufeature.c
> > +++ b/arch/riscv/kernel/cpufeature.c
> > @@ -178,6 +178,7 @@ const struct riscv_isa_ext_data riscv_isa_ext[] = {
> >       __RISCV_ISA_EXT_DATA(ssaia, RISCV_ISA_EXT_SSAIA),
> >       __RISCV_ISA_EXT_DATA(sscofpmf, RISCV_ISA_EXT_SSCOFPMF),
> >       __RISCV_ISA_EXT_DATA(sstc, RISCV_ISA_EXT_SSTC),
> > +     __RISCV_ISA_EXT_DATA(svadu, RISCV_ISA_EXT_SVADU),
> >       __RISCV_ISA_EXT_DATA(svinval, RISCV_ISA_EXT_SVINVAL),
> >       __RISCV_ISA_EXT_DATA(svnapot, RISCV_ISA_EXT_SVNAPOT),
> >       __RISCV_ISA_EXT_DATA(svpbmt, RISCV_ISA_EXT_SVPBMT),
> > --
> > 2.17.1
> >
>
> Thanks,
> drew

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Re: [PATCH v2 2/3] dt-bindings: riscv: Add Svadu Entry

[Stefan O'Rear]

On Fri, Sep 22, 2023, at 4:56 AM, Yong-Xuan Wang wrote:
> Add an entry for the Svadu extension to the riscv,isa-extensions property.
>
> Signed-off-by: Yong-Xuan Wang <yongxuan.wang@sifive.com>
> ---
>  Documentation/devicetree/bindings/riscv/extensions.yaml | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/riscv/extensions.yaml 
> b/Documentation/devicetree/bindings/riscv/extensions.yaml
> index cc1f546fdbdc..b5a0aed0165b 100644
> --- a/Documentation/devicetree/bindings/riscv/extensions.yaml
> +++ b/Documentation/devicetree/bindings/riscv/extensions.yaml
> @@ -147,6 +147,12 @@ properties:
>              ratified at commit 3f9ed34 ("Add ability to manually 
> trigger
>              workflow. (#2)") of riscv-time-compare.
> 
> +        - const: svadu
> +          description: |
> +            The standard Svadu supervisor-level extension for hardware updating
> +            of PTE A/D bits as frozen at commit b65e07c ("move to Frozen
> +            state") of riscv-svadu.
> +

This is incomplete without a specification of the behavior of the HADE bit implied
by svadu being present.

The ratified RVA20 requires page table accesses with A/D = 0 to trap, in other
words HADE = 0 for RVA20 conformance.  If we are serious about compatibility,
I think that we need platforms to be able to conform to both RVA20 and RVA23,
which requires HADE = 0 at kernel entry with a SBI call to set HADE = 1.  For
the same reason KVM should probably default to HADE = 0 so that the default
configuration remains conformant to RVA20.

-s

>          - const: svinval
>            description:
>              The standard Svinval supervisor-level extension for fine-grained
> -- 
> 2.17.1
>
>
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Re: [PATCH v2 2/3] dt-bindings: riscv: Add Svadu Entry

[Jessica Clarke]

On 27 Sep 2023, at 18:24, Stefan O'Rear <sorear@fastmail.com> wrote:
> 
> On Fri, Sep 22, 2023, at 4:56 AM, Yong-Xuan Wang wrote:
>> Add an entry for the Svadu extension to the riscv,isa-extensions property.
>> 
>> Signed-off-by: Yong-Xuan Wang <yongxuan.wang@sifive.com>
>> ---
>> Documentation/devicetree/bindings/riscv/extensions.yaml | 6 ++++++
>> 1 file changed, 6 insertions(+)
>> 
>> diff --git a/Documentation/devicetree/bindings/riscv/extensions.yaml 
>> b/Documentation/devicetree/bindings/riscv/extensions.yaml
>> index cc1f546fdbdc..b5a0aed0165b 100644
>> --- a/Documentation/devicetree/bindings/riscv/extensions.yaml
>> +++ b/Documentation/devicetree/bindings/riscv/extensions.yaml
>> @@ -147,6 +147,12 @@ properties:
>>             ratified at commit 3f9ed34 ("Add ability to manually 
>> trigger
>>             workflow. (#2)") of riscv-time-compare.
>> 
>> +        - const: svadu
>> +          description: |
>> +            The standard Svadu supervisor-level extension for hardware updating
>> +            of PTE A/D bits as frozen at commit b65e07c ("move to Frozen
>> +            state") of riscv-svadu.
>> +
> 
> This is incomplete without a specification of the behavior of the HADE bit implied
> by svadu being present.
> 
> The ratified RVA20 requires page table accesses with A/D = 0 to trap, in other
> words HADE = 0 for RVA20 conformance.  If we are serious about compatibility,
> I think that we need platforms to be able to conform to both RVA20 and RVA23,
> which requires HADE = 0 at kernel entry with a SBI call to set HADE = 1.  For
> the same reason KVM should probably default to HADE = 0 so that the default
> configuration remains conformant to RVA20.

I’ve filed https://github.com/riscv/riscv-svadu/issues/21 to track this
broken ISA design, as discussed on IRC.

As a FreeBSD RISC-V developer, and sometime reviewer of Linux RISC-V
patches, this is a NAK from me for this ISA design. Which does beg the
question of how much sense the current RISC-V processes make, given for
freezing a spec you just need to send out the relevant RFC patches,
they don’t actually need to have any review from the project in
question that says it’s a sensible design, instead treating that as
part of the public review period, where it’s much harder to
fundamentally change the spec, despite being the first time most people
see it or take it seriously as a thing to look at. In my opinion there
is a serious need for knowledgeable people on the software side to
review the ISA extension and its interaction with software *before* it
can be frozen so that these things can be fixed. And of course, if they
do get fixed during/after public review, what good is the frozen state
anyway, because a spec that changes is not very frozen.

But I’m probably preaching to the choir here about RISC-V processes
being unfit for purpose.

Jess

>>         - const: svinval
>>           description:
>>             The standard Svinval supervisor-level extension for fine-grained
>> -- 
>> 2.17.1
>> 
>> 
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> 
> _______________________________________________
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