[PATCH 0/5] Add parsing for Zimop ISA extension

[PATCH 0/5] Add parsing for Zimop ISA extension

[Clément Léger]

The Zimop ISA extension was ratified recently. This series adds support
for parsing it from riscv,isa, hwprobe export and kvm support for
Guest/VM.

Clément Léger (5):
  dt-bindings: riscv: add Zimop ISA extension description
  riscv: add ISA extension parsing for Zimop
  riscv: hwprobe: export Zimop ISA extension
  RISC-V: KVM: Allow Zimop extension for Guest/VM
  KVM: riscv: selftests: Add Zimop extension to get-reg-list test

 Documentation/arch/riscv/hwprobe.rst                    | 4 ++++
 Documentation/devicetree/bindings/riscv/extensions.yaml | 5 +++++
 arch/riscv/include/asm/hwcap.h                          | 1 +
 arch/riscv/include/uapi/asm/hwprobe.h                   | 1 +
 arch/riscv/include/uapi/asm/kvm.h                       | 1 +
 arch/riscv/kernel/cpufeature.c                          | 1 +
 arch/riscv/kernel/sys_hwprobe.c                         | 1 +
 arch/riscv/kvm/vcpu_onereg.c                            | 2 ++
 tools/testing/selftests/kvm/riscv/get-reg-list.c        | 4 ++++
 9 files changed, 20 insertions(+)

-- 
2.43.0

[PATCH 1/5] dt-bindings: riscv: add Zimop ISA extension description

[Clément Léger]

Add description for the Zimop (May-Be-Operations) ISA extension which
was ratified in commit 58220614a5f of the riscv-isa-manual.

Signed-off-by: Clément Léger <cleger@rivosinc.com>
---
 Documentation/devicetree/bindings/riscv/extensions.yaml | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/Documentation/devicetree/bindings/riscv/extensions.yaml b/Documentation/devicetree/bindings/riscv/extensions.yaml
index 468c646247aa..616370318a66 100644
--- a/Documentation/devicetree/bindings/riscv/extensions.yaml
+++ b/Documentation/devicetree/bindings/riscv/extensions.yaml
@@ -363,6 +363,11 @@ properties:
             ratified in the 20191213 version of the unprivileged ISA
             specification.
 
+        - const: zimop
+          description:
+            The standard Zimop extension version 1.0, as ratified in commit
+            58220614a5f ("Zimop is ratified/1.0") of the riscv-isa-manual.
+
         - const: ztso
           description:
             The standard Ztso extension for total store ordering, as ratified
-- 
2.43.0

Re: [PATCH 1/5] dt-bindings: riscv: add Zimop ISA extension description

[Conor Dooley]

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On Thu, Apr 04, 2024 at 12:32:47PM +0200, Clément Léger wrote:
> Add description for the Zimop (May-Be-Operations) ISA extension which
> was ratified in commit 58220614a5f of the riscv-isa-manual.
> 
> Signed-off-by: Clément Léger <cleger@rivosinc.com>

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

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[PATCH 2/5] riscv: add ISA extension parsing for Zimop

[Clément Léger]

Add parsing for Zimop ISA extension which was ratified in commit
58220614a5f of the riscv-isa-manual.

Signed-off-by: Clément Léger <cleger@rivosinc.com>
---
 arch/riscv/include/asm/hwcap.h | 1 +
 arch/riscv/kernel/cpufeature.c | 1 +
 2 files changed, 2 insertions(+)

diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
index e17d0078a651..543e3ea2da0e 100644
--- a/arch/riscv/include/asm/hwcap.h
+++ b/arch/riscv/include/asm/hwcap.h
@@ -81,6 +81,7 @@
 #define RISCV_ISA_EXT_ZTSO		72
 #define RISCV_ISA_EXT_ZACAS		73
 #define RISCV_ISA_EXT_XANDESPMU		74
+#define RISCV_ISA_EXT_ZIMOP		75
 
 #define RISCV_ISA_EXT_XLINUXENVCFG	127
 
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index 3ed2359eae35..115ba001f1bc 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -256,6 +256,7 @@ const struct riscv_isa_ext_data riscv_isa_ext[] = {
 	__RISCV_ISA_EXT_DATA(zihintntl, RISCV_ISA_EXT_ZIHINTNTL),
 	__RISCV_ISA_EXT_DATA(zihintpause, RISCV_ISA_EXT_ZIHINTPAUSE),
 	__RISCV_ISA_EXT_DATA(zihpm, RISCV_ISA_EXT_ZIHPM),
+	__RISCV_ISA_EXT_DATA(zimop, RISCV_ISA_EXT_ZIMOP),
 	__RISCV_ISA_EXT_DATA(zacas, RISCV_ISA_EXT_ZACAS),
 	__RISCV_ISA_EXT_DATA(zfa, RISCV_ISA_EXT_ZFA),
 	__RISCV_ISA_EXT_DATA(zfh, RISCV_ISA_EXT_ZFH),
-- 
2.43.0

Re: [PATCH 2/5] riscv: add ISA extension parsing for Zimop

[Conor Dooley]

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On Thu, Apr 04, 2024 at 12:32:48PM +0200, Clément Léger wrote:
> Add parsing for Zimop ISA extension which was ratified in commit
> 58220614a5f of the riscv-isa-manual.
> 
> Signed-off-by: Clément Léger <cleger@rivosinc.com>

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

> ---
>  arch/riscv/include/asm/hwcap.h | 1 +
>  arch/riscv/kernel/cpufeature.c | 1 +
>  2 files changed, 2 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> index e17d0078a651..543e3ea2da0e 100644
> --- a/arch/riscv/include/asm/hwcap.h
> +++ b/arch/riscv/include/asm/hwcap.h
> @@ -81,6 +81,7 @@
>  #define RISCV_ISA_EXT_ZTSO		72
>  #define RISCV_ISA_EXT_ZACAS		73
>  #define RISCV_ISA_EXT_XANDESPMU		74
> +#define RISCV_ISA_EXT_ZIMOP		75
>  
>  #define RISCV_ISA_EXT_XLINUXENVCFG	127
>  
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 3ed2359eae35..115ba001f1bc 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -256,6 +256,7 @@ const struct riscv_isa_ext_data riscv_isa_ext[] = {
>  	__RISCV_ISA_EXT_DATA(zihintntl, RISCV_ISA_EXT_ZIHINTNTL),
>  	__RISCV_ISA_EXT_DATA(zihintpause, RISCV_ISA_EXT_ZIHINTPAUSE),
>  	__RISCV_ISA_EXT_DATA(zihpm, RISCV_ISA_EXT_ZIHPM),
> +	__RISCV_ISA_EXT_DATA(zimop, RISCV_ISA_EXT_ZIMOP),
>  	__RISCV_ISA_EXT_DATA(zacas, RISCV_ISA_EXT_ZACAS),
>  	__RISCV_ISA_EXT_DATA(zfa, RISCV_ISA_EXT_ZFA),
>  	__RISCV_ISA_EXT_DATA(zfh, RISCV_ISA_EXT_ZFH),
> -- 
> 2.43.0
> 

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[PATCH 3/5] riscv: hwprobe: export Zimop ISA extension

[Clément Léger]

Export Zimop ISA extension through hwprobe.

Signed-off-by: Clément Léger <cleger@rivosinc.com>
---
 Documentation/arch/riscv/hwprobe.rst  | 4 ++++
 arch/riscv/include/uapi/asm/hwprobe.h | 1 +
 arch/riscv/kernel/sys_hwprobe.c       | 1 +
 3 files changed, 6 insertions(+)

diff --git a/Documentation/arch/riscv/hwprobe.rst b/Documentation/arch/riscv/hwprobe.rst
index b2bcc9eed9aa..9ca5b093b6d5 100644
--- a/Documentation/arch/riscv/hwprobe.rst
+++ b/Documentation/arch/riscv/hwprobe.rst
@@ -188,6 +188,10 @@ The following keys are defined:
        manual starting from commit 95cf1f9 ("Add changes requested by Ved
        during signoff")
 
+  * :c:macro:`RISCV_HWPROBE_EXT_ZIMOP`: The Zimop May-Be-Operations extension is
+       supported as defined in the RISC-V ISA manual starting from commit
+       58220614a5f ("Zimop is ratified/1.0").
+
 * :c:macro:`RISCV_HWPROBE_KEY_CPUPERF_0`: A bitmask that contains performance
   information about the selected set of processors.
 
diff --git a/arch/riscv/include/uapi/asm/hwprobe.h b/arch/riscv/include/uapi/asm/hwprobe.h
index 9f2a8e3ff204..ac6874ab743a 100644
--- a/arch/riscv/include/uapi/asm/hwprobe.h
+++ b/arch/riscv/include/uapi/asm/hwprobe.h
@@ -59,6 +59,7 @@ struct riscv_hwprobe {
 #define		RISCV_HWPROBE_EXT_ZTSO		(1ULL << 33)
 #define		RISCV_HWPROBE_EXT_ZACAS		(1ULL << 34)
 #define		RISCV_HWPROBE_EXT_ZICOND	(1ULL << 35)
+#define		RISCV_HWPROBE_EXT_ZIMOP		(1ULL << 36)
 #define RISCV_HWPROBE_KEY_CPUPERF_0	5
 #define		RISCV_HWPROBE_MISALIGNED_UNKNOWN	(0 << 0)
 #define		RISCV_HWPROBE_MISALIGNED_EMULATED	(1 << 0)
diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c
index 8cae41a502dd..c99a4cf231c5 100644
--- a/arch/riscv/kernel/sys_hwprobe.c
+++ b/arch/riscv/kernel/sys_hwprobe.c
@@ -111,6 +111,7 @@ static void hwprobe_isa_ext0(struct riscv_hwprobe *pair,
 		EXT_KEY(ZTSO);
 		EXT_KEY(ZACAS);
 		EXT_KEY(ZICOND);
+		EXT_KEY(ZIMOP);
 
 		if (has_vector()) {
 			EXT_KEY(ZVBB);
-- 
2.43.0

[PATCH 4/5] RISC-V: KVM: Allow Zimop extension for Guest/VM

[Clément Léger]

Extend the KVM ISA extension ONE_REG interface to allow KVM user space
to detect and enable Zimop extension for Guest/VM.

Signed-off-by: Clément Léger <cleger@rivosinc.com>
---
 arch/riscv/include/uapi/asm/kvm.h | 1 +
 arch/riscv/kvm/vcpu_onereg.c      | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
index b1c503c2959c..35a12aa1953e 100644
--- a/arch/riscv/include/uapi/asm/kvm.h
+++ b/arch/riscv/include/uapi/asm/kvm.h
@@ -167,6 +167,7 @@ enum KVM_RISCV_ISA_EXT_ID {
 	KVM_RISCV_ISA_EXT_ZFA,
 	KVM_RISCV_ISA_EXT_ZTSO,
 	KVM_RISCV_ISA_EXT_ZACAS,
+	KVM_RISCV_ISA_EXT_ZIMOP,
 	KVM_RISCV_ISA_EXT_MAX,
 };
 
diff --git a/arch/riscv/kvm/vcpu_onereg.c b/arch/riscv/kvm/vcpu_onereg.c
index f4a6124d25c9..c6ee763422f2 100644
--- a/arch/riscv/kvm/vcpu_onereg.c
+++ b/arch/riscv/kvm/vcpu_onereg.c
@@ -60,6 +60,7 @@ static const unsigned long kvm_isa_ext_arr[] = {
 	KVM_ISA_EXT_ARR(ZIHINTNTL),
 	KVM_ISA_EXT_ARR(ZIHINTPAUSE),
 	KVM_ISA_EXT_ARR(ZIHPM),
+	KVM_ISA_EXT_ARR(ZIMOP),
 	KVM_ISA_EXT_ARR(ZKND),
 	KVM_ISA_EXT_ARR(ZKNE),
 	KVM_ISA_EXT_ARR(ZKNH),
@@ -137,6 +138,7 @@ static bool kvm_riscv_vcpu_isa_disable_allowed(unsigned long ext)
 	case KVM_RISCV_ISA_EXT_ZIHINTNTL:
 	case KVM_RISCV_ISA_EXT_ZIHINTPAUSE:
 	case KVM_RISCV_ISA_EXT_ZIHPM:
+	case KVM_RISCV_ISA_EXT_ZIMOP:
 	case KVM_RISCV_ISA_EXT_ZKND:
 	case KVM_RISCV_ISA_EXT_ZKNE:
 	case KVM_RISCV_ISA_EXT_ZKNH:
-- 
2.43.0

[PATCH 5/5] KVM: riscv: selftests: Add Zimop extension to get-reg-list test

[Clément Léger]

The KVM RISC-V allows Zimop extension for Guest/VM so add this
extension to get-reg-list test.

Signed-off-by: Clément Léger <cleger@rivosinc.com>
---
 tools/testing/selftests/kvm/riscv/get-reg-list.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/testing/selftests/kvm/riscv/get-reg-list.c b/tools/testing/selftests/kvm/riscv/get-reg-list.c
index b882b7b9b785..40107bb61975 100644
--- a/tools/testing/selftests/kvm/riscv/get-reg-list.c
+++ b/tools/testing/selftests/kvm/riscv/get-reg-list.c
@@ -67,6 +67,7 @@ bool filter_reg(__u64 reg)
 	case KVM_REG_RISCV_ISA_EXT | KVM_REG_RISCV_ISA_SINGLE | KVM_RISCV_ISA_EXT_ZIHINTNTL:
 	case KVM_REG_RISCV_ISA_EXT | KVM_REG_RISCV_ISA_SINGLE | KVM_RISCV_ISA_EXT_ZIHINTPAUSE:
 	case KVM_REG_RISCV_ISA_EXT | KVM_REG_RISCV_ISA_SINGLE | KVM_RISCV_ISA_EXT_ZIHPM:
+	case KVM_REG_RISCV_ISA_EXT | KVM_REG_RISCV_ISA_SINGLE | KVM_RISCV_ISA_EXT_ZIMOP:
 	case KVM_REG_RISCV_ISA_EXT | KVM_REG_RISCV_ISA_SINGLE | KVM_RISCV_ISA_EXT_ZKND:
 	case KVM_REG_RISCV_ISA_EXT | KVM_REG_RISCV_ISA_SINGLE | KVM_RISCV_ISA_EXT_ZKNE:
 	case KVM_REG_RISCV_ISA_EXT | KVM_REG_RISCV_ISA_SINGLE | KVM_RISCV_ISA_EXT_ZKNH:
@@ -432,6 +433,7 @@ static const char *isa_ext_single_id_to_str(__u64 reg_off)
 		KVM_ISA_EXT_ARR(ZIHINTNTL),
 		KVM_ISA_EXT_ARR(ZIHINTPAUSE),
 		KVM_ISA_EXT_ARR(ZIHPM),
+		KVM_ISA_EXT_ARR(ZIMOP),
 		KVM_ISA_EXT_ARR(ZKND),
 		KVM_ISA_EXT_ARR(ZKNE),
 		KVM_ISA_EXT_ARR(ZKNH),
@@ -955,6 +957,7 @@ KVM_ISA_EXT_SIMPLE_CONFIG(zifencei, ZIFENCEI);
 KVM_ISA_EXT_SIMPLE_CONFIG(zihintntl, ZIHINTNTL);
 KVM_ISA_EXT_SIMPLE_CONFIG(zihintpause, ZIHINTPAUSE);
 KVM_ISA_EXT_SIMPLE_CONFIG(zihpm, ZIHPM);
+KVM_ISA_EXT_SIMPLE_CONFIG(zimop, ZIMOP);
 KVM_ISA_EXT_SIMPLE_CONFIG(zknd, ZKND);
 KVM_ISA_EXT_SIMPLE_CONFIG(zkne, ZKNE);
 KVM_ISA_EXT_SIMPLE_CONFIG(zknh, ZKNH);
@@ -1010,6 +1013,7 @@ struct vcpu_reg_list *vcpu_configs[] = {
 	&config_zihintntl,
 	&config_zihintpause,
 	&config_zihpm,
+	&config_zimop,
 	&config_zknd,
 	&config_zkne,
 	&config_zknh,
-- 
2.43.0

Re: [PATCH 0/5] Add parsing for Zimop ISA extension

[Andrew Jones]

On Thu, Apr 04, 2024 at 12:32:46PM +0200, Clément Léger wrote:
> The Zimop ISA extension was ratified recently. This series adds support
> for parsing it from riscv,isa, hwprobe export and kvm support for
> Guest/VM.

I'm not sure we need this. Zimop by itself isn't useful, so I don't know
if we need to advertise it at all. When an extension comes along that
redefines some MOPs, then we'll advertise that extension, but the fact
Zimop is used for that extension is really just an implementation detail.

Thanks,
drew

> 
> Clément Léger (5):
>   dt-bindings: riscv: add Zimop ISA extension description
>   riscv: add ISA extension parsing for Zimop
>   riscv: hwprobe: export Zimop ISA extension
>   RISC-V: KVM: Allow Zimop extension for Guest/VM
>   KVM: riscv: selftests: Add Zimop extension to get-reg-list test
> 
>  Documentation/arch/riscv/hwprobe.rst                    | 4 ++++
>  Documentation/devicetree/bindings/riscv/extensions.yaml | 5 +++++
>  arch/riscv/include/asm/hwcap.h                          | 1 +
>  arch/riscv/include/uapi/asm/hwprobe.h                   | 1 +
>  arch/riscv/include/uapi/asm/kvm.h                       | 1 +
>  arch/riscv/kernel/cpufeature.c                          | 1 +
>  arch/riscv/kernel/sys_hwprobe.c                         | 1 +
>  arch/riscv/kvm/vcpu_onereg.c                            | 2 ++
>  tools/testing/selftests/kvm/riscv/get-reg-list.c        | 4 ++++
>  9 files changed, 20 insertions(+)
> 
> -- 
> 2.43.0
> 
> 
> -- 
> kvm-riscv mailing list
> kvm-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/kvm-riscv

Re: [PATCH 0/5] Add parsing for Zimop ISA extension

[Deepak Gupta]

On Fri, Apr 5, 2024 at 8:26 AM Andrew Jones <ajones@ventanamicro.com> wrote:
>
> On Thu, Apr 04, 2024 at 12:32:46PM +0200, Clément Léger wrote:
> > The Zimop ISA extension was ratified recently. This series adds support
> > for parsing it from riscv,isa, hwprobe export and kvm support for
> > Guest/VM.
>
> I'm not sure we need this. Zimop by itself isn't useful, so I don't know
> if we need to advertise it at all. When an extension comes along that
> redefines some MOPs, then we'll advertise that extension, but the fact
> Zimop is used for that extension is really just an implementation detail.

Only situation I see this can be useful is this:--

An implementer, implemented Zimops in CPU solely for the purpose that they can
run mainline distro & packages on their hardware and don't want to leverage any
feature which are built on top of Zimop.

As an example zicfilp and zicfiss are dependent on zimops. glibc can
do following

1) check elf header if binary was compiled with zicfiss and zicfilp,
if yes goto step 2, else goto step 6.
2) check if zicfiss/zicfilp is available in hw via hwprobe, if yes
goto step 5. else goto step 3
3) check if zimop is available via hwprobe, if yes goto step 6, else goto step 4
4) This binary won't be able to run successfully on this platform,
issue exit syscall. <-- termination
5) issue prctl to enable shadow stack and landing pad for current task
<-- enable feature
6) let the binary run <-- let the binary run because no harm can be done

Re: [PATCH 0/5] Add parsing for Zimop ISA extension

[Clément Léger]

On 05/04/2024 19:33, Deepak Gupta wrote:
> On Fri, Apr 5, 2024 at 8:26 AM Andrew Jones <ajones@ventanamicro.com> wrote:
>>
>> On Thu, Apr 04, 2024 at 12:32:46PM +0200, Clément Léger wrote:
>>> The Zimop ISA extension was ratified recently. This series adds support
>>> for parsing it from riscv,isa, hwprobe export and kvm support for
>>> Guest/VM.
>>
>> I'm not sure we need this. Zimop by itself isn't useful, so I don't know
>> if we need to advertise it at all. When an extension comes along that
>> redefines some MOPs, then we'll advertise that extension, but the fact
>> Zimop is used for that extension is really just an implementation detail.
> 
> Only situation I see this can be useful is this:--
> 
> An implementer, implemented Zimops in CPU solely for the purpose that they can
> run mainline distro & packages on their hardware and don't want to leverage any
> feature which are built on top of Zimop.

Yes, the rationale was that some binaries using extensions that overload
MOPs could still be run. With Zimop exposed, the loader could determine
if the binary can be executed without potentially crashing. We could
also let the program run anyway but the execution could potentially
crash unexpectedly, which IMHO is not really good for the user
experience nor for debugging. I already think that the segfaults which
happens when executing binaries that need some missing extension are not
so easy to debug, so better add more guards.

> 
> As an example zicfilp and zicfiss are dependent on zimops. glibc can
> do following
> 
> 1) check elf header if binary was compiled with zicfiss and zicfilp,
> if yes goto step 2, else goto step 6.
> 2) check if zicfiss/zicfilp is available in hw via hwprobe, if yes
> goto step 5. else goto step 3
> 3) check if zimop is available via hwprobe, if yes goto step 6, else goto step 4

I think you meant step 5 rather than step 6.

Clément

> 4) This binary won't be able to run successfully on this platform,
> issue exit syscall. <-- termination
> 5) issue prctl to enable shadow stack and landing pad for current task
> <-- enable feature
> 6) let the binary run <-- let the binary run because no harm can be done

Re: [PATCH 0/5] Add parsing for Zimop ISA extension

[Andrew Jones]

On Mon, Apr 08, 2024 at 10:01:12AM +0200, Clément Léger wrote:
> 
> 
> On 05/04/2024 19:33, Deepak Gupta wrote:
> > On Fri, Apr 5, 2024 at 8:26 AM Andrew Jones <ajones@ventanamicro.com> wrote:
> >>
> >> On Thu, Apr 04, 2024 at 12:32:46PM +0200, Clément Léger wrote:
> >>> The Zimop ISA extension was ratified recently. This series adds support
> >>> for parsing it from riscv,isa, hwprobe export and kvm support for
> >>> Guest/VM.
> >>
> >> I'm not sure we need this. Zimop by itself isn't useful, so I don't know
> >> if we need to advertise it at all. When an extension comes along that
> >> redefines some MOPs, then we'll advertise that extension, but the fact
> >> Zimop is used for that extension is really just an implementation detail.
> > 
> > Only situation I see this can be useful is this:--
> > 
> > An implementer, implemented Zimops in CPU solely for the purpose that they can
> > run mainline distro & packages on their hardware and don't want to leverage any
> > feature which are built on top of Zimop.
> 
> Yes, the rationale was that some binaries using extensions that overload
> MOPs could still be run. With Zimop exposed, the loader could determine
> if the binary can be executed without potentially crashing. We could
> also let the program run anyway but the execution could potentially
> crash unexpectedly, which IMHO is not really good for the user
> experience nor for debugging. I already think that the segfaults which
> happens when executing binaries that need some missing extension are not
> so easy to debug, so better add more guards.

OK. It's only one more extension out of dozens, so I won't complain more,
but I was thinking that binaries that use particular extensions would
check for those particular extensions (step 2), rather than Zimop.

Thanks,
drew

> 
> > 
> > As an example zicfilp and zicfiss are dependent on zimops. glibc can
> > do following
> > 
> > 1) check elf header if binary was compiled with zicfiss and zicfilp,
> > if yes goto step 2, else goto step 6.
> > 2) check if zicfiss/zicfilp is available in hw via hwprobe, if yes
> > goto step 5. else goto step 3
> > 3) check if zimop is available via hwprobe, if yes goto step 6, else goto step 4
> 
> I think you meant step 5 rather than step 6.
> 
> Clément
> 
> > 4) This binary won't be able to run successfully on this platform,
> > issue exit syscall. <-- termination
> > 5) issue prctl to enable shadow stack and landing pad for current task
> > <-- enable feature
> > 6) let the binary run <-- let the binary run because no harm can be done

Re: [PATCH 0/5] Add parsing for Zimop ISA extension

[Clément Léger]

On 08/04/2024 13:03, Andrew Jones wrote:
> On Mon, Apr 08, 2024 at 10:01:12AM +0200, Clément Léger wrote:
>>
>>
>> On 05/04/2024 19:33, Deepak Gupta wrote:
>>> On Fri, Apr 5, 2024 at 8:26 AM Andrew Jones <ajones@ventanamicro.com> wrote:
>>>>
>>>> On Thu, Apr 04, 2024 at 12:32:46PM +0200, Clément Léger wrote:
>>>>> The Zimop ISA extension was ratified recently. This series adds support
>>>>> for parsing it from riscv,isa, hwprobe export and kvm support for
>>>>> Guest/VM.
>>>>
>>>> I'm not sure we need this. Zimop by itself isn't useful, so I don't know
>>>> if we need to advertise it at all. When an extension comes along that
>>>> redefines some MOPs, then we'll advertise that extension, but the fact
>>>> Zimop is used for that extension is really just an implementation detail.
>>>
>>> Only situation I see this can be useful is this:--
>>>
>>> An implementer, implemented Zimops in CPU solely for the purpose that they can
>>> run mainline distro & packages on their hardware and don't want to leverage any
>>> feature which are built on top of Zimop.
>>
>> Yes, the rationale was that some binaries using extensions that overload
>> MOPs could still be run. With Zimop exposed, the loader could determine
>> if the binary can be executed without potentially crashing. We could
>> also let the program run anyway but the execution could potentially
>> crash unexpectedly, which IMHO is not really good for the user
>> experience nor for debugging. I already think that the segfaults which
>> happens when executing binaries that need some missing extension are not
>> so easy to debug, so better add more guards.
> 
> OK. It's only one more extension out of dozens, so I won't complain more,

No worries, your point *is* valid since I'm not sure yet that the loader
will actually do that one day.

BTW, are you aware of any effort to make the elf dynamic loader
"smarter" and actually check for needed extensions to be present rather
than blindly running the elf and potentially catching SIGILL ?

Thanks,

Clément

> but I was thinking that binaries that use particular extensions would
> check for those particular extensions (step 2), rather than Zimop.
> 
> Thanks,
> drew
> 
>>
>>>
>>> As an example zicfilp and zicfiss are dependent on zimops. glibc can
>>> do following
>>>
>>> 1) check elf header if binary was compiled with zicfiss and zicfilp,
>>> if yes goto step 2, else goto step 6.
>>> 2) check if zicfiss/zicfilp is available in hw via hwprobe, if yes
>>> goto step 5. else goto step 3
>>> 3) check if zimop is available via hwprobe, if yes goto step 6, else goto step 4
>>
>> I think you meant step 5 rather than step 6.
>>
>> Clément
>>
>>> 4) This binary won't be able to run successfully on this platform,
>>> issue exit syscall. <-- termination
>>> 5) issue prctl to enable shadow stack and landing pad for current task
>>> <-- enable feature
>>> 6) let the binary run <-- let the binary run because no harm can be done

Re: [PATCH 0/5] Add parsing for Zimop ISA extension

[Andrew Jones]

On Mon, Apr 08, 2024 at 01:19:39PM +0200, Clément Léger wrote:
> 
> 
> On 08/04/2024 13:03, Andrew Jones wrote:
> > On Mon, Apr 08, 2024 at 10:01:12AM +0200, Clément Léger wrote:
> >>
> >>
> >> On 05/04/2024 19:33, Deepak Gupta wrote:
> >>> On Fri, Apr 5, 2024 at 8:26 AM Andrew Jones <ajones@ventanamicro.com> wrote:
> >>>>
> >>>> On Thu, Apr 04, 2024 at 12:32:46PM +0200, Clément Léger wrote:
> >>>>> The Zimop ISA extension was ratified recently. This series adds support
> >>>>> for parsing it from riscv,isa, hwprobe export and kvm support for
> >>>>> Guest/VM.
> >>>>
> >>>> I'm not sure we need this. Zimop by itself isn't useful, so I don't know
> >>>> if we need to advertise it at all. When an extension comes along that
> >>>> redefines some MOPs, then we'll advertise that extension, but the fact
> >>>> Zimop is used for that extension is really just an implementation detail.
> >>>
> >>> Only situation I see this can be useful is this:--
> >>>
> >>> An implementer, implemented Zimops in CPU solely for the purpose that they can
> >>> run mainline distro & packages on their hardware and don't want to leverage any
> >>> feature which are built on top of Zimop.
> >>
> >> Yes, the rationale was that some binaries using extensions that overload
> >> MOPs could still be run. With Zimop exposed, the loader could determine
> >> if the binary can be executed without potentially crashing. We could
> >> also let the program run anyway but the execution could potentially
> >> crash unexpectedly, which IMHO is not really good for the user
> >> experience nor for debugging. I already think that the segfaults which
> >> happens when executing binaries that need some missing extension are not
> >> so easy to debug, so better add more guards.
> > 
> > OK. It's only one more extension out of dozens, so I won't complain more,
> 
> No worries, your point *is* valid since I'm not sure yet that the loader
> will actually do that one day.
> 
> BTW, are you aware of any effort to make the elf dynamic loader
> "smarter" and actually check for needed extensions to be present rather
> than blindly running the elf and potentially catching SIGILL ?

Jeff Law told me a bit about FMV (function multiversioning). I don't know
much about this, but, from what he's told me, it sounds like there will be
an ifunc resolver which invokes hwprobe to determine which variants are
possible/best to use, so it should be possible to avoid SIGILL by always
having a basic variant.

Thanks,
drew

> 
> Thanks,
> 
> Clément
> 
> > but I was thinking that binaries that use particular extensions would
> > check for those particular extensions (step 2), rather than Zimop.
> > 
> > Thanks,
> > drew
> > 
> >>
> >>>
> >>> As an example zicfilp and zicfiss are dependent on zimops. glibc can
> >>> do following
> >>>
> >>> 1) check elf header if binary was compiled with zicfiss and zicfilp,
> >>> if yes goto step 2, else goto step 6.
> >>> 2) check if zicfiss/zicfilp is available in hw via hwprobe, if yes
> >>> goto step 5. else goto step 3
> >>> 3) check if zimop is available via hwprobe, if yes goto step 6, else goto step 4
> >>
> >> I think you meant step 5 rather than step 6.
> >>
> >> Clément
> >>
> >>> 4) This binary won't be able to run successfully on this platform,
> >>> issue exit syscall. <-- termination
> >>> 5) issue prctl to enable shadow stack and landing pad for current task
> >>> <-- enable feature
> >>> 6) let the binary run <-- let the binary run because no harm can be done

Re: [PATCH 0/5] Add parsing for Zimop ISA extension

[Deepak Gupta]

On Mon, Apr 08, 2024 at 10:01:12AM +0200, Clément Léger wrote:
>
>
>On 05/04/2024 19:33, Deepak Gupta wrote:
>> On Fri, Apr 5, 2024 at 8:26 AM Andrew Jones <ajones@ventanamicro.com> wrote:
>>>
>>> On Thu, Apr 04, 2024 at 12:32:46PM +0200, Clément Léger wrote:
>>>> The Zimop ISA extension was ratified recently. This series adds support
>>>> for parsing it from riscv,isa, hwprobe export and kvm support for
>>>> Guest/VM.
>>>
>>> I'm not sure we need this. Zimop by itself isn't useful, so I don't know
>>> if we need to advertise it at all. When an extension comes along that
>>> redefines some MOPs, then we'll advertise that extension, but the fact
>>> Zimop is used for that extension is really just an implementation detail.
>>
>> Only situation I see this can be useful is this:--
>>
>> An implementer, implemented Zimops in CPU solely for the purpose that they can
>> run mainline distro & packages on their hardware and don't want to leverage any
>> feature which are built on top of Zimop.
>
>Yes, the rationale was that some binaries using extensions that overload
>MOPs could still be run. With Zimop exposed, the loader could determine
>if the binary can be executed without potentially crashing. We could
>also let the program run anyway but the execution could potentially
>crash unexpectedly, which IMHO is not really good for the user
>experience nor for debugging. I already think that the segfaults which
>happens when executing binaries that need some missing extension are not
>so easy to debug, so better add more guards.
>
>>
>> As an example zicfilp and zicfiss are dependent on zimops. glibc can
>> do following
>>
>> 1) check elf header if binary was compiled with zicfiss and zicfilp,
>> if yes goto step 2, else goto step 6.
>> 2) check if zicfiss/zicfilp is available in hw via hwprobe, if yes
>> goto step 5. else goto step 3
>> 3) check if zimop is available via hwprobe, if yes goto step 6, else goto step 4
>
>I think you meant step 5 rather than step 6.

No I did mean step 6 which is let the binary run. Step 5 is "issue the prctl" to
light up the feature, this should have been reached via step 2 if feature was
available.

Going to step 6 from step 3 basically means that underlying hardware only supports
zimops and thus this binary is safe to run on this hardware. But no need to issue
any prctl to kernel to enable this feature.

>
>Clément
>
>> 4) This binary won't be able to run successfully on this platform,
>> issue exit syscall. <-- termination
>> 5) issue prctl to enable shadow stack and landing pad for current task
>> <-- enable feature
>> 6) let the binary run <-- let the binary run because no harm can be done

Re: [PATCH 0/5] Add parsing for Zimop ISA extension

[Andrew Jones]

On Thu, Apr 04, 2024 at 12:32:46PM +0200, Clément Léger wrote:
> The Zimop ISA extension was ratified recently. This series adds support
> for parsing it from riscv,isa, hwprobe export and kvm support for
> Guest/VM.
> 
> Clément Léger (5):
>   dt-bindings: riscv: add Zimop ISA extension description
>   riscv: add ISA extension parsing for Zimop
>   riscv: hwprobe: export Zimop ISA extension
>   RISC-V: KVM: Allow Zimop extension for Guest/VM
>   KVM: riscv: selftests: Add Zimop extension to get-reg-list test
> 
>  Documentation/arch/riscv/hwprobe.rst                    | 4 ++++
>  Documentation/devicetree/bindings/riscv/extensions.yaml | 5 +++++
>  arch/riscv/include/asm/hwcap.h                          | 1 +
>  arch/riscv/include/uapi/asm/hwprobe.h                   | 1 +
>  arch/riscv/include/uapi/asm/kvm.h                       | 1 +
>  arch/riscv/kernel/cpufeature.c                          | 1 +
>  arch/riscv/kernel/sys_hwprobe.c                         | 1 +
>  arch/riscv/kvm/vcpu_onereg.c                            | 2 ++
>  tools/testing/selftests/kvm/riscv/get-reg-list.c        | 4 ++++
>  9 files changed, 20 insertions(+)
> 
> -- 
> 2.43.0

For the series,

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