[RFC V1 PATCH 1/5] x86: kvm: HACK: Allow testing of priv memfd approach

[Vishal Annapurve]

Add plumbing in KVM logic to allow private memfd series:
https://lore.kernel.org/linux-mm/20220310140911.50924-1-chao.p.peng@xxxxxxxxxxxxxxx/
to be tested with non-confidential VMs.

1) Existing hypercall KVM_HC_MAP_GPA_RANGE is modified to support
marking pages of the guest memory as privately accessed or
accessed in a shared fashion.

2) kvm_vcpu_is_private_gfn is defined to allow guest accesses to
be categorized as shared or private based on the values set by
KVM_HC_MAP_GPA_RANGE hypercall.

3) KVM_MEM_PRIVATE flag for memslots is marked as always supported.

Signed-off-by: Vishal Annapurve <vannapurve@xxxxxxxxxx>
---
 arch/x86/include/uapi/asm/kvm_para.h |  1 +
 arch/x86/kvm/mmu/mmu.c               |  9 +++++----
 arch/x86/kvm/x86.c                   | 16 ++++++++++++++--
 include/linux/kvm_host.h             |  3 +++
 virt/kvm/kvm_main.c                  |  2 +-
 5 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h
index 6e64b27b2c1e..3bc9add4095d 100644
--- a/arch/x86/include/uapi/asm/kvm_para.h
+++ b/arch/x86/include/uapi/asm/kvm_para.h
@@ -102,6 +102,7 @@ struct kvm_clock_pairing {
 #define KVM_MAP_GPA_RANGE_PAGE_SZ_2M	(1 << 0)
 #define KVM_MAP_GPA_RANGE_PAGE_SZ_1G	(1 << 1)
 #define KVM_MAP_GPA_RANGE_ENC_STAT(n)	(n << 4)
+#define KVM_MARK_GPA_RANGE_ENC_ACCESS	(1 << 8)
 #define KVM_MAP_GPA_RANGE_ENCRYPTED	KVM_MAP_GPA_RANGE_ENC_STAT(1)
 #define KVM_MAP_GPA_RANGE_DECRYPTED	KVM_MAP_GPA_RANGE_ENC_STAT(0)
 
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index b1a30a751db0..ee9bc36011de 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3895,10 +3895,11 @@ static bool kvm_arch_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 
 static bool kvm_vcpu_is_private_gfn(struct kvm_vcpu *vcpu, gfn_t gfn)
 {
-	/*
-	 * At this time private gfn has not been supported yet. Other patch
-	 * that enables it should change this.
-	 */
+	gpa_t priv_gfn_end = vcpu->priv_gfn + vcpu->priv_pages;
+
+	if ((gfn >= vcpu->priv_gfn) && (gfn < priv_gfn_end))
+		return true;
+
 	return false;
 }
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 11a949928a85..3b17fa7f2192 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9186,8 +9186,20 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
 		if (!(vcpu->kvm->arch.hypercall_exit_enabled & (1 << KVM_HC_MAP_GPA_RANGE)))
 			break;
 
-		if (!PAGE_ALIGNED(gpa) || !npages ||
-		    gpa_to_gfn(gpa) + npages <= gpa_to_gfn(gpa)) {
+		if (!PAGE_ALIGNED(gpa) ||
+			gpa_to_gfn(gpa) + npages < gpa_to_gfn(gpa)) {
+			ret = -KVM_EINVAL;
+			break;
+		}
+
+		if (attrs & KVM_MARK_GPA_RANGE_ENC_ACCESS) {
+			vcpu->priv_gfn = gpa_to_gfn(gpa);
+			vcpu->priv_pages = npages;
+			ret = 0;
+			break;
+		}
+
+		if (!npages) {
 			ret = -KVM_EINVAL;
 			break;
 		}
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 0150e952a131..7c12a0bdb495 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -311,6 +311,9 @@ struct kvm_vcpu {
 	u64 requests;
 	unsigned long guest_debug;
 
+	uint64_t priv_gfn;
+	uint64_t priv_pages;
+
 	struct mutex mutex;
 	struct kvm_run *run;
 
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index df5311755a40..a31a58aa1b79 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1487,7 +1487,7 @@ static void kvm_replace_memslot(struct kvm *kvm,
 
 bool __weak kvm_arch_private_memory_supported(struct kvm *kvm)
 {
-	return false;
+	return true;
 }
 
 static int check_memory_region_flags(struct kvm *kvm,
-- 
2.35.1.1178.g4f1659d476-goog