The arch specific code may need to validate a gpa range if it is a shared
memory between the host and the guest. Currently, there are few places
where it is used in RISC-V implementation. Given the nature of the function
it may be used for other architectures. Hence, a common helper function
is added.

Signed-off-by: Atish Patra <atishp@rivosinc.com>
---
 include/linux/kvm_host.h |  2 ++
 virt/kvm/kvm_main.c      | 21 +++++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 291d49b9bf05..adda61cc4072 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1383,6 +1383,8 @@ static inline int kvm_vcpu_map_readonly(struct kvm_vcpu *vcpu, gpa_t gpa,
 
 unsigned long kvm_vcpu_gfn_to_hva(struct kvm_vcpu *vcpu, gfn_t gfn);
 unsigned long kvm_vcpu_gfn_to_hva_prot(struct kvm_vcpu *vcpu, gfn_t gfn, bool *writable);
+int kvm_vcpu_validate_gpa_range(struct kvm_vcpu *vcpu, gpa_t gpa, unsigned long len,
+				bool write_access);
 int kvm_vcpu_read_guest_page(struct kvm_vcpu *vcpu, gfn_t gfn, void *data, int offset,
 			     int len);
 int kvm_vcpu_read_guest_atomic(struct kvm_vcpu *vcpu, gpa_t gpa, void *data,
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e85b33a92624..3f52f5571fa6 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3301,6 +3301,27 @@ int kvm_vcpu_write_guest(struct kvm_vcpu *vcpu, gpa_t gpa, const void *data,
 }
 EXPORT_SYMBOL_GPL(kvm_vcpu_write_guest);
 
+int kvm_vcpu_validate_gpa_range(struct kvm_vcpu *vcpu, gpa_t gpa, unsigned long len,
+				bool write_access)
+{
+	gfn_t gfn = gpa >> PAGE_SHIFT;
+	int seg;
+	int offset = offset_in_page(gpa);
+	bool writable = false;
+	unsigned long hva;
+
+	while ((seg = next_segment(len, offset)) != 0) {
+		hva = kvm_vcpu_gfn_to_hva_prot(vcpu, gfn, &writable);
+		if (kvm_is_error_hva(hva) || (writable ^ write_access))
+			return -EPERM;
+		offset = 0;
+		len -= seg;
+		++gfn;
+	}
+	return 0;
+}
+EXPORT_SYMBOL_GPL(kvm_vcpu_validate_gpa_range);
+
 static int __kvm_gfn_to_hva_cache_init(struct kvm_memslots *slots,
 				       struct gfn_to_hva_cache *ghc,
 				       gpa_t gpa, unsigned long len)

-- 
2.43.0

Hi Paolo,

On Fri, May 23, 2025 at 12:33 AM Atish Patra <atishp@rivosinc.com> wrote:
>
> The arch specific code may need to validate a gpa range if it is a shared
> memory between the host and the guest. Currently, there are few places
> where it is used in RISC-V implementation. Given the nature of the function
> it may be used for other architectures. Hence, a common helper function
> is added.
>
> Signed-off-by: Atish Patra <atishp@rivosinc.com>
> ---
>  include/linux/kvm_host.h |  2 ++
>  virt/kvm/kvm_main.c      | 21 +++++++++++++++++++++
>  2 files changed, 23 insertions(+)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 291d49b9bf05..adda61cc4072 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -1383,6 +1383,8 @@ static inline int kvm_vcpu_map_readonly(struct kvm_vcpu *vcpu, gpa_t gpa,
>
>  unsigned long kvm_vcpu_gfn_to_hva(struct kvm_vcpu *vcpu, gfn_t gfn);
>  unsigned long kvm_vcpu_gfn_to_hva_prot(struct kvm_vcpu *vcpu, gfn_t gfn, bool *writable);
> +int kvm_vcpu_validate_gpa_range(struct kvm_vcpu *vcpu, gpa_t gpa, unsigned long len,
> +                               bool write_access);
>  int kvm_vcpu_read_guest_page(struct kvm_vcpu *vcpu, gfn_t gfn, void *data, int offset,
>                              int len);
>  int kvm_vcpu_read_guest_atomic(struct kvm_vcpu *vcpu, gpa_t gpa, void *data,
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index e85b33a92624..3f52f5571fa6 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -3301,6 +3301,27 @@ int kvm_vcpu_write_guest(struct kvm_vcpu *vcpu, gpa_t gpa, const void *data,
>  }
>  EXPORT_SYMBOL_GPL(kvm_vcpu_write_guest);
>
> +int kvm_vcpu_validate_gpa_range(struct kvm_vcpu *vcpu, gpa_t gpa, unsigned long len,
> +                               bool write_access)
> +{
> +       gfn_t gfn = gpa >> PAGE_SHIFT;
> +       int seg;
> +       int offset = offset_in_page(gpa);
> +       bool writable = false;
> +       unsigned long hva;
> +
> +       while ((seg = next_segment(len, offset)) != 0) {
> +               hva = kvm_vcpu_gfn_to_hva_prot(vcpu, gfn, &writable);
> +               if (kvm_is_error_hva(hva) || (writable ^ write_access))
> +                       return -EPERM;
> +               offset = 0;
> +               len -= seg;
> +               ++gfn;
> +       }
> +       return 0;
> +}
> +EXPORT_SYMBOL_GPL(kvm_vcpu_validate_gpa_range);
> +

Can you please review this common helper since it is in virt/kvm ?

>  static int __kvm_gfn_to_hva_cache_init(struct kvm_memslots *slots,
>                                        struct gfn_to_hva_cache *ghc,
>                                        gpa_t gpa, unsigned long len)
>
> --
> 2.43.0
>

Regards,
Anup

On Fri, May 23, 2025 at 12:33 AM Atish Patra <atishp@rivosinc.com> wrote:
>
> The arch specific code may need to validate a gpa range if it is a shared
> memory between the host and the guest. Currently, there are few places
> where it is used in RISC-V implementation. Given the nature of the function
> it may be used for other architectures. Hence, a common helper function
> is added.
>
> Signed-off-by: Atish Patra <atishp@rivosinc.com>
> ---
>  include/linux/kvm_host.h |  2 ++
>  virt/kvm/kvm_main.c      | 21 +++++++++++++++++++++
>  2 files changed, 23 insertions(+)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 291d49b9bf05..adda61cc4072 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -1383,6 +1383,8 @@ static inline int kvm_vcpu_map_readonly(struct kvm_vcpu *vcpu, gpa_t gpa,
>
>  unsigned long kvm_vcpu_gfn_to_hva(struct kvm_vcpu *vcpu, gfn_t gfn);
>  unsigned long kvm_vcpu_gfn_to_hva_prot(struct kvm_vcpu *vcpu, gfn_t gfn, bool *writable);
> +int kvm_vcpu_validate_gpa_range(struct kvm_vcpu *vcpu, gpa_t gpa, unsigned long len,
> +                               bool write_access);
>  int kvm_vcpu_read_guest_page(struct kvm_vcpu *vcpu, gfn_t gfn, void *data, int offset,
>                              int len);
>  int kvm_vcpu_read_guest_atomic(struct kvm_vcpu *vcpu, gpa_t gpa, void *data,
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index e85b33a92624..3f52f5571fa6 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -3301,6 +3301,27 @@ int kvm_vcpu_write_guest(struct kvm_vcpu *vcpu, gpa_t gpa, const void *data,
>  }
>  EXPORT_SYMBOL_GPL(kvm_vcpu_write_guest);
>
> +int kvm_vcpu_validate_gpa_range(struct kvm_vcpu *vcpu, gpa_t gpa, unsigned long len,
> +                               bool write_access)
> +{
> +       gfn_t gfn = gpa >> PAGE_SHIFT;
> +       int seg;
> +       int offset = offset_in_page(gpa);
> +       bool writable = false;
> +       unsigned long hva;

Nit: rearrange the variables in a inverted pyramid shape.

> +
> +       while ((seg = next_segment(len, offset)) != 0) {
> +               hva = kvm_vcpu_gfn_to_hva_prot(vcpu, gfn, &writable);
> +               if (kvm_is_error_hva(hva) || (writable ^ write_access))
> +                       return -EPERM;
> +               offset = 0;
> +               len -= seg;
> +               ++gfn;
> +       }
> +       return 0;
> +}
> +EXPORT_SYMBOL_GPL(kvm_vcpu_validate_gpa_range);
> +
>  static int __kvm_gfn_to_hva_cache_init(struct kvm_memslots *slots,
>                                        struct gfn_to_hva_cache *ghc,
>                                        gpa_t gpa, unsigned long len)
>
> --
> 2.43.0
>

Otherwise, looks good to me.

Reviewed-by: Anup Patel <anup@brainfault.org>

Regards,
Anup