Re: [PATCH 5/6] KVM: x86: Implement kvm_arch_vcpu_pre_fault_memory()

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On 4/19/2024 4:59 PM, Paolo Bonzini wrote:
From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>

Wire KVM_PRE_FAULT_MEMORY ioctl to __kvm_mmu_do_page_fault() to populate guest
memory.  It can be called right after KVM_CREATE_VCPU creates a vCPU,
since at that point kvm_mmu_create() and kvm_init_mmu() are called and
the vCPU is ready to invoke the KVM page fault handler.

The helper function kvm_mmu_map_tdp_page take care of the logic to
process RET_PF_* return values and convert them to success or errno.

Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
Message-ID: <9b866a0ae7147f96571c439e75429a03dcb659b6.1712785629.git.isaku.yamahata@xxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
  arch/x86/kvm/Kconfig   |  1 +
  arch/x86/kvm/mmu/mmu.c | 72 ++++++++++++++++++++++++++++++++++++++++++
  arch/x86/kvm/x86.c     |  3 ++
  3 files changed, 76 insertions(+)

diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 7632fe6e4db9..54c155432793 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -44,6 +44,7 @@ config KVM
  	select KVM_VFIO
  	select HAVE_KVM_PM_NOTIFIER if PM
  	select KVM_GENERIC_HARDWARE_ENABLING
+	select KVM_GENERIC_PRE_FAULT_MEMORY
  	help
  	  Support hosting fully virtualized guest machines using hardware
  	  virtualization extensions.  You will need a fairly recent
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 10e90788b263..a045b23964c0 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4647,6 +4647,78 @@ int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
  	return direct_page_fault(vcpu, fault);
  }
+static int kvm_tdp_map_page(struct kvm_vcpu *vcpu, gpa_t gpa, u64 error_code,
+		     u8 *level)
+{
+	int r;
+
+	/* Restrict to TDP page fault. */
+	if (vcpu->arch.mmu->page_fault != kvm_tdp_page_fault)
+		return -EOPNOTSUPP;
+
+retry:
+	r = __kvm_mmu_do_page_fault(vcpu, gpa, error_code, true, NULL, level);
+	if (r < 0)
+		return r;
+
+	switch (r) {
+	case RET_PF_RETRY:
+		if (signal_pending(current))
+			return -EINTR;
+		cond_resched();
+		goto retry;
+
+	case RET_PF_FIXED:
+	case RET_PF_SPURIOUS:
+		break;
+
+	case RET_PF_EMULATE:
+		return -ENOENT;
+
+	case RET_PF_CONTINUE:
+	case RET_PF_INVALID:
+	default:
+		WARN_ON_ONCE(r);
+		return -EIO;

Need to update patch 1 for -EIO

+	}
+
+	return 0;
+}
+
+long kvm_arch_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu,
+				    struct kvm_pre_fault_memory *range)
+{
+	u64 error_code = PFERR_GUEST_FINAL_MASK;
+	u8 level = PG_LEVEL_4K;
+	u64 end;
+	int r;
+
+	/*
+	 * reload is efficient when called repeatedly, so we can do it on
+	 * every iteration.
+	 */
+	kvm_mmu_reload(vcpu);
+
+	if (kvm_arch_has_private_mem(vcpu->kvm) &&
+	    kvm_mem_is_private(vcpu->kvm, gpa_to_gfn(range->gpa)))
+		error_code |= PFERR_PRIVATE_ACCESS;
+
+	/*
+	 * Shadow paging uses GVA for kvm page fault, so restrict to
+	 * two-dimensional paging.
+	 */
+	r = kvm_tdp_map_page(vcpu, range->gpa, error_code, &level);
+	if (r < 0)
+		return r;
+
+	/*
+	 * If the mapping that covers range->gpa can use a huge page, it
+	 * may start below it or end after range->gpa + range->size.
+	 */
+	end = (range->gpa & KVM_HPAGE_MASK(level)) + KVM_HPAGE_SIZE(level);
+	return min(range->size, end - range->gpa);
+}
+
  static void nonpaging_init_context(struct kvm_mmu *context)
  {
  	context->page_fault = nonpaging_page_fault;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 83b8260443a3..619ad713254e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4715,6 +4715,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
  	case KVM_CAP_MEMORY_FAULT_INFO:
  		r = 1;
  		break;
+	case KVM_CAP_PRE_FAULT_MEMORY:
+		r = tdp_enabled;
+		break;
  	case KVM_CAP_EXIT_HYPERCALL:
  		r = KVM_EXIT_HYPERCALL_VALID_MASK;
  		break;





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