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

From: Vishal Annapurve
Date: Fri Apr 08 2022 - 17:06:11 EST


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