[PATCH V2] RISC-V: KVM: Write hgatp register with valid mode bits

[PATCH V2] RISC-V: KVM: Write hgatp register with valid mode bits

[fangyu.yu]

From: Fangyu Yu <fangyu.yu@linux.alibaba.com>

According to the RISC-V Privileged Architecture Spec, when MODE=Bare
is selected,software must write zero to the remaining fields of hgatp.

We have detected the valid mode supported by the HW before, So using a
valid mode to detect how many vmid bits are supported.

Signed-off-by: Fangyu Yu <fangyu.yu@linux.alibaba.com>

---
Changes in v2:
- Fixed build error since kvm_riscv_gstage_mode() has been modified.
---
 arch/riscv/kvm/vmid.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kvm/vmid.c b/arch/riscv/kvm/vmid.c
index 3b426c800480..5f33625f4070 100644
--- a/arch/riscv/kvm/vmid.c
+++ b/arch/riscv/kvm/vmid.c
@@ -14,6 +14,7 @@
 #include <linux/smp.h>
 #include <linux/kvm_host.h>
 #include <asm/csr.h>
+#include <asm/kvm_mmu.h>
 #include <asm/kvm_tlb.h>
 #include <asm/kvm_vmid.h>
 
@@ -28,7 +29,7 @@ void __init kvm_riscv_gstage_vmid_detect(void)
 
 	/* Figure-out number of VMID bits in HW */
 	old = csr_read(CSR_HGATP);
-	csr_write(CSR_HGATP, old | HGATP_VMID);
+	csr_write(CSR_HGATP, (kvm_riscv_gstage_mode << HGATP_MODE_SHIFT) | HGATP_VMID);
 	vmid_bits = csr_read(CSR_HGATP);
 	vmid_bits = (vmid_bits & HGATP_VMID) >> HGATP_VMID_SHIFT;
 	vmid_bits = fls_long(vmid_bits);
-- 
2.49.0


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Re: [PATCH V2] RISC-V: KVM: Write hgatp register with valid mode bits

[Guo Ren]

On Mon, Aug 18, 2025 at 1:42 PM <fangyu.yu@linux.alibaba.com> wrote:
>
> From: Fangyu Yu <fangyu.yu@linux.alibaba.com>
>
> According to the RISC-V Privileged Architecture Spec, when MODE=Bare
> is selected,software must write zero to the remaining fields of hgatp.
>
> We have detected the valid mode supported by the HW before, So using a
> valid mode to detect how many vmid bits are supported.
Good catch! It's a bug. The code seems copied from asids_init(), whose
old value is not bare mode. For real hardware, it would cause
problems, but the qemu buggy code hides the problem.

It needs a tag: Fixes: fd7bb4a251df ("RISC-V: KVM: Implement VMID allocator")

Others, Reviewed-by: Guo Ren <guoren@kerenl.org>

>
> Signed-off-by: Fangyu Yu <fangyu.yu@linux.alibaba.com>
>
> ---
> Changes in v2:
> - Fixed build error since kvm_riscv_gstage_mode() has been modified.
> ---
>  arch/riscv/kvm/vmid.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/kvm/vmid.c b/arch/riscv/kvm/vmid.c
> index 3b426c800480..5f33625f4070 100644
> --- a/arch/riscv/kvm/vmid.c
> +++ b/arch/riscv/kvm/vmid.c
> @@ -14,6 +14,7 @@
>  #include <linux/smp.h>
>  #include <linux/kvm_host.h>
>  #include <asm/csr.h>
> +#include <asm/kvm_mmu.h>
>  #include <asm/kvm_tlb.h>
>  #include <asm/kvm_vmid.h>
>
> @@ -28,7 +29,7 @@ void __init kvm_riscv_gstage_vmid_detect(void)
>
>         /* Figure-out number of VMID bits in HW */
>         old = csr_read(CSR_HGATP);
> -       csr_write(CSR_HGATP, old | HGATP_VMID);
> +       csr_write(CSR_HGATP, (kvm_riscv_gstage_mode << HGATP_MODE_SHIFT) | HGATP_VMID);
>         vmid_bits = csr_read(CSR_HGATP);
>         vmid_bits = (vmid_bits & HGATP_VMID) >> HGATP_VMID_SHIFT;
>         vmid_bits = fls_long(vmid_bits);
> --
> 2.49.0
>


-- 
Best Regards
 Guo Ren

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Re: [PATCH V2] RISC-V: KVM: Write hgatp register with valid mode bits

[Guo Ren]

On Mon, Aug 18, 2025 at 2:17 PM Guo Ren <guoren@kernel.org> wrote:
>
> On Mon, Aug 18, 2025 at 1:42 PM <fangyu.yu@linux.alibaba.com> wrote:
> >
> > From: Fangyu Yu <fangyu.yu@linux.alibaba.com>
> >
> > According to the RISC-V Privileged Architecture Spec, when MODE=Bare
> > is selected,software must write zero to the remaining fields of hgatp.
> >
> > We have detected the valid mode supported by the HW before, So using a
> > valid mode to detect how many vmid bits are supported.
> Good catch! It's a bug. The code seems copied from asids_init(), whose
> old value is not bare mode. For real hardware, it would cause
> problems, but the qemu buggy code hides the problem.
>
> It needs a tag: Fixes: fd7bb4a251df ("RISC-V: KVM: Implement VMID allocator")
>
> Others, Reviewed-by: Guo Ren <guoren@kerenl.org>

Sorry for the typo:
Reviewed-by: Guo Ren <guoren@kernel.org>
                                                             ^^
>
> >
> > Signed-off-by: Fangyu Yu <fangyu.yu@linux.alibaba.com>
> >
> > ---
> > Changes in v2:
> > - Fixed build error since kvm_riscv_gstage_mode() has been modified.
> > ---
> >  arch/riscv/kvm/vmid.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/riscv/kvm/vmid.c b/arch/riscv/kvm/vmid.c
> > index 3b426c800480..5f33625f4070 100644
> > --- a/arch/riscv/kvm/vmid.c
> > +++ b/arch/riscv/kvm/vmid.c
> > @@ -14,6 +14,7 @@
> >  #include <linux/smp.h>
> >  #include <linux/kvm_host.h>
> >  #include <asm/csr.h>
> > +#include <asm/kvm_mmu.h>
> >  #include <asm/kvm_tlb.h>
> >  #include <asm/kvm_vmid.h>
> >
> > @@ -28,7 +29,7 @@ void __init kvm_riscv_gstage_vmid_detect(void)
> >
> >         /* Figure-out number of VMID bits in HW */
> >         old = csr_read(CSR_HGATP);
> > -       csr_write(CSR_HGATP, old | HGATP_VMID);
> > +       csr_write(CSR_HGATP, (kvm_riscv_gstage_mode << HGATP_MODE_SHIFT) | HGATP_VMID);
> >         vmid_bits = csr_read(CSR_HGATP);
> >         vmid_bits = (vmid_bits & HGATP_VMID) >> HGATP_VMID_SHIFT;
> >         vmid_bits = fls_long(vmid_bits);
> > --
> > 2.49.0
> >
>
>
> --
> Best Regards
>  Guo Ren



-- 
Best Regards
 Guo Ren

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[PATCH] RISC-V KVM: Remove unnecessary HGATP csr_read

[guoren]

From: "Guo Ren (Alibaba DAMO Academy)" <guoren@kernel.org>

The HGATP has been set to zero in gstage_mode_detect(), so there
is no need to save the old context. Unify the code convention
with gstage_mode_detect().

Signed-off-by: Guo Ren (Alibaba DAMO Academy) <guoren@kernel.org>
---
This cleanup is based on yufang.yu's vmid fixup patch.
---
 arch/riscv/kvm/vmid.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/arch/riscv/kvm/vmid.c b/arch/riscv/kvm/vmid.c
index 5f33625f4070..abb1c2bf2542 100644
--- a/arch/riscv/kvm/vmid.c
+++ b/arch/riscv/kvm/vmid.c
@@ -25,15 +25,12 @@ static DEFINE_SPINLOCK(vmid_lock);
 
 void __init kvm_riscv_gstage_vmid_detect(void)
 {
-	unsigned long old;
-
 	/* Figure-out number of VMID bits in HW */
-	old = csr_read(CSR_HGATP);
 	csr_write(CSR_HGATP, (kvm_riscv_gstage_mode << HGATP_MODE_SHIFT) | HGATP_VMID);
 	vmid_bits = csr_read(CSR_HGATP);
 	vmid_bits = (vmid_bits & HGATP_VMID) >> HGATP_VMID_SHIFT;
 	vmid_bits = fls_long(vmid_bits);
-	csr_write(CSR_HGATP, old);
+	csr_write(CSR_HGATP, 0);
 
 	/* We polluted local TLB so flush all guest TLB */
 	kvm_riscv_local_hfence_gvma_all();
-- 
2.40.1


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[PATCH V4 0/3] Fixup & optimize hgatp mode & vmid detect functions

[guoren]

From: "Guo Ren (Alibaba DAMO Academy)" <guoren@kernel.org>

Here are serval fixup & optmizitions for hgatp detect according to the RISC-V Privileged Architecture Spec.

---
Changes in v4:
 - Involve ("RISC-V: KVM: Prevent HGATP_MODE_BARE passed"), which
   explain why gstage_mode_detect needs reset HGATP to zero.
 
Changes in v3:
 - Add "Fixes" tag.
 - Involve("RISC-V: KVM: Remove unnecessary HGATP csr_read"), which
   depends on patch 1.

Changes in v2:
 - Fixed build error since kvm_riscv_gstage_mode() has been modified.
---

Fangyu Yu (1):
  RISC-V: KVM: Write hgatp register with valid mode bits

Guo Ren (Alibaba DAMO Academy) (2):
  RISC-V: KVM: Remove unnecessary HGATP csr_read
  RISC-V: KVM: Prevent HGATP_MODE_BARE passed

 arch/riscv/kvm/gstage.c | 27 ++++++++++++++++++++++++---
 arch/riscv/kvm/main.c   | 35 +++++++++++++++++------------------
 arch/riscv/kvm/vmid.c   |  8 +++-----
 3 files changed, 44 insertions(+), 26 deletions(-)

-- 
2.40.1


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[PATCH V4 1/3] RISC-V: KVM: Write hgatp register with valid mode bits

[guoren]

From: Fangyu Yu <fangyu.yu@linux.alibaba.com>

According to the RISC-V Privileged Architecture Spec, when MODE=Bare
is selected,software must write zero to the remaining fields of hgatp.

We have detected the valid mode supported by the HW before, So using a
valid mode to detect how many vmid bits are supported.

Fixes: fd7bb4a251df ("RISC-V: KVM: Implement VMID allocator")
Reviewed-by: Nutty Liu <nutty.liu@hotmail.com>
Reviewed-by: Troy Mitchell <troy.mitchell@linux.spacemit.com>
Reviewed-by: Guo Ren (Alibaba DAMO Academy) <guoren@kernel.org>
Signed-off-by: Fangyu Yu <fangyu.yu@linux.alibaba.com>
Signed-off-by: Guo Ren (Alibaba DAMO Academy) <guoren@kernel.org>
---
 arch/riscv/kvm/vmid.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kvm/vmid.c b/arch/riscv/kvm/vmid.c
index 3b426c800480..5f33625f4070 100644
--- a/arch/riscv/kvm/vmid.c
+++ b/arch/riscv/kvm/vmid.c
@@ -14,6 +14,7 @@
 #include <linux/smp.h>
 #include <linux/kvm_host.h>
 #include <asm/csr.h>
+#include <asm/kvm_mmu.h>
 #include <asm/kvm_tlb.h>
 #include <asm/kvm_vmid.h>
 
@@ -28,7 +29,7 @@ void __init kvm_riscv_gstage_vmid_detect(void)
 
 	/* Figure-out number of VMID bits in HW */
 	old = csr_read(CSR_HGATP);
-	csr_write(CSR_HGATP, old | HGATP_VMID);
+	csr_write(CSR_HGATP, (kvm_riscv_gstage_mode << HGATP_MODE_SHIFT) | HGATP_VMID);
 	vmid_bits = csr_read(CSR_HGATP);
 	vmid_bits = (vmid_bits & HGATP_VMID) >> HGATP_VMID_SHIFT;
 	vmid_bits = fls_long(vmid_bits);
-- 
2.40.1


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[PATCH V4 2/3] RISC-V: KVM: Remove unnecessary HGATP csr_read

[guoren]

From: "Guo Ren (Alibaba DAMO Academy)" <guoren@kernel.org>

The HGATP has been set to zero in gstage_mode_detect(), so there
is no need to save the old context. Unify the code convention
with gstage_mode_detect().

Signed-off-by: Fangyu Yu <fangyu.yu@linux.alibaba.com>
Signed-off-by: Guo Ren (Alibaba DAMO Academy) <guoren@kernel.org>
---
 arch/riscv/kvm/vmid.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/arch/riscv/kvm/vmid.c b/arch/riscv/kvm/vmid.c
index 5f33625f4070..abb1c2bf2542 100644
--- a/arch/riscv/kvm/vmid.c
+++ b/arch/riscv/kvm/vmid.c
@@ -25,15 +25,12 @@ static DEFINE_SPINLOCK(vmid_lock);
 
 void __init kvm_riscv_gstage_vmid_detect(void)
 {
-	unsigned long old;
-
 	/* Figure-out number of VMID bits in HW */
-	old = csr_read(CSR_HGATP);
 	csr_write(CSR_HGATP, (kvm_riscv_gstage_mode << HGATP_MODE_SHIFT) | HGATP_VMID);
 	vmid_bits = csr_read(CSR_HGATP);
 	vmid_bits = (vmid_bits & HGATP_VMID) >> HGATP_VMID_SHIFT;
 	vmid_bits = fls_long(vmid_bits);
-	csr_write(CSR_HGATP, old);
+	csr_write(CSR_HGATP, 0);
 
 	/* We polluted local TLB so flush all guest TLB */
 	kvm_riscv_local_hfence_gvma_all();
-- 
2.40.1


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[PATCH V4 3/3] RISC-V: KVM: Prevent HGATP_MODE_BARE passed

[guoren]

From: "Guo Ren (Alibaba DAMO Academy)" <guoren@kernel.org>

urrent kvm_riscv_gstage_mode_detect() assumes H-extension must
have HGATP_MODE_SV39X4/SV32X4 at least, but the spec allows
H-extension with HGATP_MODE_BARE alone. The KVM depends on
!HGATP_MODE_BARE at least, so enhance the gstage-mode-detect
to block HGATP_MODE_BARE.

Move gstage-mode-check closer to gstage-mode-detect to prevent
unnecessary init.

Reviewed-by: Troy Mitchell <troy.mitchell@linux.dev>
Reviewed-by: Nutty Liu <nutty.liu@hotmail.com>
Signed-off-by: Guo Ren (Alibaba DAMO Academy) <guoren@kernel.org>
---
 arch/riscv/kvm/gstage.c | 27 ++++++++++++++++++++++++---
 arch/riscv/kvm/main.c   | 35 +++++++++++++++++------------------
 2 files changed, 41 insertions(+), 21 deletions(-)

diff --git a/arch/riscv/kvm/gstage.c b/arch/riscv/kvm/gstage.c
index 24c270d6d0e2..b67d60d722c2 100644
--- a/arch/riscv/kvm/gstage.c
+++ b/arch/riscv/kvm/gstage.c
@@ -321,7 +321,7 @@ void __init kvm_riscv_gstage_mode_detect(void)
 	if ((csr_read(CSR_HGATP) >> HGATP_MODE_SHIFT) == HGATP_MODE_SV57X4) {
 		kvm_riscv_gstage_mode = HGATP_MODE_SV57X4;
 		kvm_riscv_gstage_pgd_levels = 5;
-		goto skip_sv48x4_test;
+		goto done;
 	}
 
 	/* Try Sv48x4 G-stage mode */
@@ -329,10 +329,31 @@ void __init kvm_riscv_gstage_mode_detect(void)
 	if ((csr_read(CSR_HGATP) >> HGATP_MODE_SHIFT) == HGATP_MODE_SV48X4) {
 		kvm_riscv_gstage_mode = HGATP_MODE_SV48X4;
 		kvm_riscv_gstage_pgd_levels = 4;
+		goto done;
 	}
-skip_sv48x4_test:
 
+	/* Try Sv39x4 G-stage mode */
+	csr_write(CSR_HGATP, HGATP_MODE_SV39X4 << HGATP_MODE_SHIFT);
+	if ((csr_read(CSR_HGATP) >> HGATP_MODE_SHIFT) == HGATP_MODE_SV39X4) {
+		kvm_riscv_gstage_mode = HGATP_MODE_SV39X4;
+		kvm_riscv_gstage_pgd_levels = 3;
+		goto done;
+	}
+#else /* CONFIG_32BIT */
+	/* Try Sv32x4 G-stage mode */
+	csr_write(CSR_HGATP, HGATP_MODE_SV32X4 << HGATP_MODE_SHIFT);
+	if ((csr_read(CSR_HGATP) >> HGATP_MODE_SHIFT) == HGATP_MODE_SV32X4) {
+		kvm_riscv_gstage_mode = HGATP_MODE_SV32X4;
+		kvm_riscv_gstage_pgd_levels = 2;
+		goto done;
+	}
+#endif
+
+	/* KVM depends on !HGATP_MODE_OFF */
+	kvm_riscv_gstage_mode = HGATP_MODE_OFF;
+	kvm_riscv_gstage_pgd_levels = 0;
+
+done:
 	csr_write(CSR_HGATP, 0);
 	kvm_riscv_local_hfence_gvma_all();
-#endif
 }
diff --git a/arch/riscv/kvm/main.c b/arch/riscv/kvm/main.c
index 67c876de74ef..8ee7aaa74ddc 100644
--- a/arch/riscv/kvm/main.c
+++ b/arch/riscv/kvm/main.c
@@ -93,6 +93,23 @@ static int __init riscv_kvm_init(void)
 		return rc;
 
 	kvm_riscv_gstage_mode_detect();
+	switch (kvm_riscv_gstage_mode) {
+	case HGATP_MODE_SV32X4:
+		str = "Sv32x4";
+		break;
+	case HGATP_MODE_SV39X4:
+		str = "Sv39x4";
+		break;
+	case HGATP_MODE_SV48X4:
+		str = "Sv48x4";
+		break;
+	case HGATP_MODE_SV57X4:
+		str = "Sv57x4";
+		break;
+	default:
+		return -ENODEV;
+	}
+	kvm_info("using %s G-stage page table format\n", str);
 
 	kvm_riscv_gstage_vmid_detect();
 
@@ -135,24 +152,6 @@ static int __init riscv_kvm_init(void)
 			 (rc) ? slist : "no features");
 	}
 
-	switch (kvm_riscv_gstage_mode) {
-	case HGATP_MODE_SV32X4:
-		str = "Sv32x4";
-		break;
-	case HGATP_MODE_SV39X4:
-		str = "Sv39x4";
-		break;
-	case HGATP_MODE_SV48X4:
-		str = "Sv48x4";
-		break;
-	case HGATP_MODE_SV57X4:
-		str = "Sv57x4";
-		break;
-	default:
-		return -ENODEV;
-	}
-	kvm_info("using %s G-stage page table format\n", str);
-
 	kvm_info("VMID %ld bits available\n", kvm_riscv_gstage_vmid_bits());
 
 	if (kvm_riscv_aia_available())
-- 
2.40.1


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Re: [PATCH V2] RISC-V: KVM: Write hgatp register with valid mode bits

[Troy Mitchell]

On Mon, Aug 18, 2025 at 01:42:07PM +0800, fangyu.yu@linux.alibaba.com wrote:
> From: Fangyu Yu <fangyu.yu@linux.alibaba.com>
> 
> According to the RISC-V Privileged Architecture Spec, when MODE=Bare
> is selected,software must write zero to the remaining fields of hgatp.
> 
> We have detected the valid mode supported by the HW before, So using a
> valid mode to detect how many vmid bits are supported.
> 
> Signed-off-by: Fangyu Yu <fangyu.yu@linux.alibaba.com>
With Fixed tag, feel free to add:

Reviewed-by: Troy Mitchell <troy.mitchell@linux.spacemit.com>
> 
> ---
> Changes in v2:
> - Fixed build error since kvm_riscv_gstage_mode() has been modified.
> ---
>  arch/riscv/kvm/vmid.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/kvm/vmid.c b/arch/riscv/kvm/vmid.c
> index 3b426c800480..5f33625f4070 100644
> --- a/arch/riscv/kvm/vmid.c
> +++ b/arch/riscv/kvm/vmid.c
> @@ -14,6 +14,7 @@
>  #include <linux/smp.h>
>  #include <linux/kvm_host.h>
>  #include <asm/csr.h>
> +#include <asm/kvm_mmu.h>
>  #include <asm/kvm_tlb.h>
>  #include <asm/kvm_vmid.h>
>  
> @@ -28,7 +29,7 @@ void __init kvm_riscv_gstage_vmid_detect(void)
>  
>  	/* Figure-out number of VMID bits in HW */
>  	old = csr_read(CSR_HGATP);
> -	csr_write(CSR_HGATP, old | HGATP_VMID);
> +	csr_write(CSR_HGATP, (kvm_riscv_gstage_mode << HGATP_MODE_SHIFT) | HGATP_VMID);
>  	vmid_bits = csr_read(CSR_HGATP);
>  	vmid_bits = (vmid_bits & HGATP_VMID) >> HGATP_VMID_SHIFT;
>  	vmid_bits = fls_long(vmid_bits);
> -- 
> 2.49.0
> 
> 
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Re: [PATCH V2] RISC-V: KVM: Write hgatp register with valid mode bits

[Nutty.Liu]

On 8/18/2025 1:42 PM, fangyu.yu@linux.alibaba.com wrote:
> From: Fangyu Yu <fangyu.yu@linux.alibaba.com>
>
> According to the RISC-V Privileged Architecture Spec, when MODE=Bare
> is selected,software must write zero to the remaining fields of hgatp.
>
> We have detected the valid mode supported by the HW before, So using a
> valid mode to detect how many vmid bits are supported.
>
> Signed-off-by: Fangyu Yu <fangyu.yu@linux.alibaba.com>
>
> ---
> Changes in v2:
> - Fixed build error since kvm_riscv_gstage_mode() has been modified.
> ---
>   arch/riscv/kvm/vmid.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
Reviewed-by: Nutty Liu <nutty.liu@hotmail.com>

Thanks,
Nutty
> diff --git a/arch/riscv/kvm/vmid.c b/arch/riscv/kvm/vmid.c
> index 3b426c800480..5f33625f4070 100644
> --- a/arch/riscv/kvm/vmid.c
> +++ b/arch/riscv/kvm/vmid.c
> @@ -14,6 +14,7 @@
>   #include <linux/smp.h>
>   #include <linux/kvm_host.h>
>   #include <asm/csr.h>
> +#include <asm/kvm_mmu.h>
>   #include <asm/kvm_tlb.h>
>   #include <asm/kvm_vmid.h>
>   
> @@ -28,7 +29,7 @@ void __init kvm_riscv_gstage_vmid_detect(void)
>   
>   	/* Figure-out number of VMID bits in HW */
>   	old = csr_read(CSR_HGATP);
> -	csr_write(CSR_HGATP, old | HGATP_VMID);
> +	csr_write(CSR_HGATP, (kvm_riscv_gstage_mode << HGATP_MODE_SHIFT) | HGATP_VMID);
>   	vmid_bits = csr_read(CSR_HGATP);
>   	vmid_bits = (vmid_bits & HGATP_VMID) >> HGATP_VMID_SHIFT;
>   	vmid_bits = fls_long(vmid_bits);

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