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[RFC PATCH 5/8] KVM: x86/mmu: Introduce kvm_mmu_map_page() for prepopulating guest memory

isaku.yamahata@intel.com posted 8 patches 1 year, 11 months ago
[RFC PATCH 5/8] KVM: x86/mmu: Introduce kvm_mmu_map_page() for prepopulating guest memory
Posted by isaku.yamahata@intel.com 1 year, 11 months ago 
From: Isaku Yamahata <isaku.yamahata@intel.com>

Introduce a helper function to call kvm fault handler.  This allows
a new ioctl to invoke kvm fault handler to populate without seeing
RET_PF_* enums or other KVM MMU internal definitions.

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
---
 arch/x86/kvm/mmu.h     |  3 +++
 arch/x86/kvm/mmu/mmu.c | 30 ++++++++++++++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 60f21bb4c27b..48870c5e08ec 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -183,6 +183,9 @@ static inline void kvm_mmu_refresh_passthrough_bits(struct kvm_vcpu *vcpu,
 	__kvm_mmu_refresh_passthrough_bits(vcpu, mmu);
 }
 
+int kvm_mmu_map_page(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
+		     u8 max_level, u8 *goal_level);
+
 /*
  * Check if a given access (described through the I/D, W/R and U/S bits of a
  * page fault error code pfec) causes a permission fault with the given PTE
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index e4cc7f764980..7d5e80d17977 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4659,6 +4659,36 @@ int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 	return direct_page_fault(vcpu, fault);
 }
 
+int kvm_mmu_map_page(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
+		     u8 max_level, u8 *goal_level)
+{
+	struct kvm_page_fault fault = KVM_PAGE_FAULT_INIT(vcpu, gpa, error_code,
+							  false, max_level);
+	int r;
+
+	r = __kvm_mmu_do_page_fault(vcpu, &fault);
+
+	if (is_error_noslot_pfn(fault.pfn) || vcpu->kvm->vm_bugged)
+		return -EFAULT;
+
+	switch (r) {
+	case RET_PF_RETRY:
+		return -EAGAIN;
+
+	case RET_PF_FIXED:
+	case RET_PF_SPURIOUS:
+		*goal_level = fault.goal_level;
+		return 0;
+
+	case RET_PF_CONTINUE:
+	case RET_PF_EMULATE:
+	case RET_PF_INVALID:
+	default:
+		return -EIO;
+	}
+}
+EXPORT_SYMBOL_GPL(kvm_mmu_map_page);
+
 static void nonpaging_init_context(struct kvm_mmu *context)
 {
 	context->page_fault = nonpaging_page_fault;
-- 
2.25.1
Re: [RFC PATCH 5/8] KVM: x86/mmu: Introduce kvm_mmu_map_page() for prepopulating guest memory
Posted by Sean Christopherson 1 year, 11 months ago 
On Fri, Mar 01, 2024, isaku.yamahata@intel.com wrote:
> From: Isaku Yamahata <isaku.yamahata@intel.com>
> 
> Introduce a helper function to call kvm fault handler.  This allows
> a new ioctl to invoke kvm fault handler to populate without seeing
> RET_PF_* enums or other KVM MMU internal definitions.
> 
> Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> ---
>  arch/x86/kvm/mmu.h     |  3 +++
>  arch/x86/kvm/mmu/mmu.c | 30 ++++++++++++++++++++++++++++++
>  2 files changed, 33 insertions(+)
> 
> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> index 60f21bb4c27b..48870c5e08ec 100644
> --- a/arch/x86/kvm/mmu.h
> +++ b/arch/x86/kvm/mmu.h
> @@ -183,6 +183,9 @@ static inline void kvm_mmu_refresh_passthrough_bits(struct kvm_vcpu *vcpu,
>  	__kvm_mmu_refresh_passthrough_bits(vcpu, mmu);
>  }
>  
> +int kvm_mmu_map_page(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
> +		     u8 max_level, u8 *goal_level);
> +
>  /*
>   * Check if a given access (described through the I/D, W/R and U/S bits of a
>   * page fault error code pfec) causes a permission fault with the given PTE
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index e4cc7f764980..7d5e80d17977 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4659,6 +4659,36 @@ int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
>  	return direct_page_fault(vcpu, fault);
>  }
>  
> +int kvm_mmu_map_page(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
> +		     u8 max_level, u8 *goal_level)
> +{
> +	struct kvm_page_fault fault = KVM_PAGE_FAULT_INIT(vcpu, gpa, error_code,
> +							  false, max_level);
> +	int r;
> +
> +	r = __kvm_mmu_do_page_fault(vcpu, &fault);
> +
> +	if (is_error_noslot_pfn(fault.pfn) || vcpu->kvm->vm_bugged)
> +		return -EFAULT;

This clobbers a non-zero 'r'.  And KVM return -EIO if the VM is bugged/dead, not
-EFAULT.  I also don't see why KVM needs to explicitly check is_error_noslot_pfn(),
that should be funneled to RET_PF_EMULATE.

> +
> +	switch (r) {
> +	case RET_PF_RETRY:
> +		return -EAGAIN;
> +
> +	case RET_PF_FIXED:
> +	case RET_PF_SPURIOUS:
> +		*goal_level = fault.goal_level;
> +		return 0;
> +
> +	case RET_PF_CONTINUE:
> +	case RET_PF_EMULATE:

-EINVAL woud be more appropriate for RET_PF_EMULATE.

> +	case RET_PF_INVALID:

CONTINUE and INVALID should be WARN conditions.

> +	default:
> +		return -EIO;
> +	}
> +}
> +EXPORT_SYMBOL_GPL(kvm_mmu_map_page);

Unnecessary export.

> +
>  static void nonpaging_init_context(struct kvm_mmu *context)
>  {
>  	context->page_fault = nonpaging_page_fault;
> -- 
> 2.25.1
>
Re: [RFC PATCH 5/8] KVM: x86/mmu: Introduce kvm_mmu_map_page() for prepopulating guest memory
Posted by Isaku Yamahata 1 year, 11 months ago 
On Mon, Mar 11, 2024 at 10:29:01AM -0700,
Sean Christopherson <seanjc@google.com> wrote:

> On Fri, Mar 01, 2024, isaku.yamahata@intel.com wrote:
> > From: Isaku Yamahata <isaku.yamahata@intel.com>
> > 
> > Introduce a helper function to call kvm fault handler.  This allows
> > a new ioctl to invoke kvm fault handler to populate without seeing
> > RET_PF_* enums or other KVM MMU internal definitions.
> > 
> > Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> > ---
> >  arch/x86/kvm/mmu.h     |  3 +++
> >  arch/x86/kvm/mmu/mmu.c | 30 ++++++++++++++++++++++++++++++
> >  2 files changed, 33 insertions(+)
> > 
> > diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> > index 60f21bb4c27b..48870c5e08ec 100644
> > --- a/arch/x86/kvm/mmu.h
> > +++ b/arch/x86/kvm/mmu.h
> > @@ -183,6 +183,9 @@ static inline void kvm_mmu_refresh_passthrough_bits(struct kvm_vcpu *vcpu,
> >  	__kvm_mmu_refresh_passthrough_bits(vcpu, mmu);
> >  }
> >  
> > +int kvm_mmu_map_page(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
> > +		     u8 max_level, u8 *goal_level);
> > +
> >  /*
> >   * Check if a given access (described through the I/D, W/R and U/S bits of a
> >   * page fault error code pfec) causes a permission fault with the given PTE
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index e4cc7f764980..7d5e80d17977 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -4659,6 +4659,36 @@ int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> >  	return direct_page_fault(vcpu, fault);
> >  }
> >  
> > +int kvm_mmu_map_page(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
> > +		     u8 max_level, u8 *goal_level)
> > +{
> > +	struct kvm_page_fault fault = KVM_PAGE_FAULT_INIT(vcpu, gpa, error_code,
> > +							  false, max_level);
> > +	int r;
> > +
> > +	r = __kvm_mmu_do_page_fault(vcpu, &fault);
> > +
> > +	if (is_error_noslot_pfn(fault.pfn) || vcpu->kvm->vm_bugged)
> > +		return -EFAULT;
> 
> This clobbers a non-zero 'r'.  And KVM return -EIO if the VM is bugged/dead, not
> -EFAULT.  I also don't see why KVM needs to explicitly check is_error_noslot_pfn(),
> that should be funneled to RET_PF_EMULATE.

I'll drop this check.

> > +
> > +	switch (r) {
> > +	case RET_PF_RETRY:
> > +		return -EAGAIN;
> > +
> > +	case RET_PF_FIXED:
> > +	case RET_PF_SPURIOUS:
> > +		*goal_level = fault.goal_level;
> > +		return 0;
> > +
> > +	case RET_PF_CONTINUE:
> > +	case RET_PF_EMULATE:
> 
> -EINVAL woud be more appropriate for RET_PF_EMULATE.
> 
> > +	case RET_PF_INVALID:
> 
> CONTINUE and INVALID should be WARN conditions.

Will update them.
-- 
Isaku Yamahata <isaku.yamahata@intel.com>
Re: [RFC PATCH 5/8] KVM: x86/mmu: Introduce kvm_mmu_map_page() for prepopulating guest memory
Posted by David Matlack 1 year, 11 months ago 
On 2024-03-01 09:28 AM, isaku.yamahata@intel.com wrote:
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index e4cc7f764980..7d5e80d17977 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4659,6 +4659,36 @@ int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
>  	return direct_page_fault(vcpu, fault);
>  }
>  
> +int kvm_mmu_map_page(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
> +		     u8 max_level, u8 *goal_level)
> +{
> +	struct kvm_page_fault fault = KVM_PAGE_FAULT_INIT(vcpu, gpa, error_code,
> +							  false, max_level);
> +	int r;
> +
> +	r = __kvm_mmu_do_page_fault(vcpu, &fault);

If TDP is disabled __kvm_mmu_do_page_fault() will interpret @gpa as a
GVA no? And if the vCPU is in guest-mode __kvm_mmu_do_page_fault() will
interpret gpa as a nGPA right?
Re: [RFC PATCH 5/8] KVM: x86/mmu: Introduce kvm_mmu_map_page() for prepopulating guest memory
Posted by Isaku Yamahata 1 year, 10 months ago 
On Wed, Mar 06, 2024 at 04:38:53PM -0800,
David Matlack <dmatlack@google.com> wrote:

> On 2024-03-01 09:28 AM, isaku.yamahata@intel.com wrote:
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index e4cc7f764980..7d5e80d17977 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -4659,6 +4659,36 @@ int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> >  	return direct_page_fault(vcpu, fault);
> >  }
> >  
> > +int kvm_mmu_map_page(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
> > +		     u8 max_level, u8 *goal_level)
> > +{
> > +	struct kvm_page_fault fault = KVM_PAGE_FAULT_INIT(vcpu, gpa, error_code,
> > +							  false, max_level);
> > +	int r;
> > +
> > +	r = __kvm_mmu_do_page_fault(vcpu, &fault);
> 
> If TDP is disabled __kvm_mmu_do_page_fault() will interpret @gpa as a
> GVA no? And if the vCPU is in guest-mode __kvm_mmu_do_page_fault() will
> interpret gpa as a nGPA right?

Just to close the discussion.
As we discussed at [1], I'd lie to restrict the API to TDP MMU only
(with the next version).  If vCPU is in guest-mode or legacy MMU mode, it will
get error.

[1] https://lore.kernel.org/kvm/ZekQFdPlU7RDVt-B@google.com/
-- 
Isaku Yamahata <isaku.yamahata@intel.com>

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