aboutsummaryrefslogtreecommitdiff
diff options
context:
space:
mode:
authorPaolo Bonzini2024-03-09 11:20:44 -0500
committerPaolo Bonzini2024-03-09 11:42:17 -0500
commit39fee313fdd489480eb2c453535ab73672c39a27 (patch)
treead213f2466882fe81e760eba3092c1e112e6ea19
parent1b6c146df555bcfb9ad55dbb745ee364a9a0159f (diff)
parent2dfd2383034421101300a3b7325cf339a182d218 (diff)
Merge tag 'kvm-x86-guest_memfd_fixes-6.8' of https://github.com/kvm-x86/linux into HEAD
KVM GUEST_MEMFD fixes for 6.8: - Make KVM_MEM_GUEST_MEMFD mutually exclusive with KVM_MEM_READONLY to avoid creating ABI that KVM can't sanely support. - Update documentation for KVM_SW_PROTECTED_VM to make it abundantly clear that such VMs are purely a development and testing vehicle, and come with zero guarantees. - Limit KVM_SW_PROTECTED_VM guests to the TDP MMU, as the long term plan is to support confidential VMs with deterministic private memory (SNP and TDX) only in the TDP MMU. - Fix a bug in a GUEST_MEMFD negative test that resulted in false passes when verifying that KVM_MEM_GUEST_MEMFD memslots can't be dirty logged.
-rw-r--r--Documentation/virt/kvm/api.rst5
-rw-r--r--arch/x86/kvm/Kconfig7
-rw-r--r--arch/x86/kvm/x86.c2
-rw-r--r--tools/testing/selftests/kvm/set_memory_region_test.c12
-rw-r--r--virt/kvm/kvm_main.c8
5 files changed, 28 insertions, 6 deletions
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 3ec0b7a455a0..09c7e585ff58 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -8791,6 +8791,11 @@ means the VM type with value @n is supported. Possible values of @n are::
#define KVM_X86_DEFAULT_VM 0
#define KVM_X86_SW_PROTECTED_VM 1
+Note, KVM_X86_SW_PROTECTED_VM is currently only for development and testing.
+Do not use KVM_X86_SW_PROTECTED_VM for "real" VMs, and especially not in
+production. The behavior and effective ABI for software-protected VMs is
+unstable.
+
9. Known KVM API problems
=========================
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 87e3da7b0439..65ed14b6540b 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -80,9 +80,10 @@ config KVM_SW_PROTECTED_VM
depends on KVM && X86_64
select KVM_GENERIC_PRIVATE_MEM
help
- Enable support for KVM software-protected VMs. Currently "protected"
- means the VM can be backed with memory provided by
- KVM_CREATE_GUEST_MEMFD.
+ Enable support for KVM software-protected VMs. Currently, software-
+ protected VMs are purely a development and testing vehicle for
+ KVM_CREATE_GUEST_MEMFD. Attempting to run a "real" VM workload as a
+ software-protected VM will fail miserably.
If unsure, say "N".
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e4270eaa33df..e02cc710f56d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4580,7 +4580,7 @@ static bool kvm_is_vm_type_supported(unsigned long type)
{
return type == KVM_X86_DEFAULT_VM ||
(type == KVM_X86_SW_PROTECTED_VM &&
- IS_ENABLED(CONFIG_KVM_SW_PROTECTED_VM) && tdp_enabled);
+ IS_ENABLED(CONFIG_KVM_SW_PROTECTED_VM) && tdp_mmu_enabled);
}
int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
diff --git a/tools/testing/selftests/kvm/set_memory_region_test.c b/tools/testing/selftests/kvm/set_memory_region_test.c
index 40337f566eeb..06b43ed23580 100644
--- a/tools/testing/selftests/kvm/set_memory_region_test.c
+++ b/tools/testing/selftests/kvm/set_memory_region_test.c
@@ -367,11 +367,21 @@ static void test_invalid_memory_region_flags(void)
}
if (supported_flags & KVM_MEM_GUEST_MEMFD) {
+ int guest_memfd = vm_create_guest_memfd(vm, MEM_REGION_SIZE, 0);
+
r = __vm_set_user_memory_region2(vm, 0,
KVM_MEM_LOG_DIRTY_PAGES | KVM_MEM_GUEST_MEMFD,
- 0, MEM_REGION_SIZE, NULL, 0, 0);
+ 0, MEM_REGION_SIZE, NULL, guest_memfd, 0);
TEST_ASSERT(r && errno == EINVAL,
"KVM_SET_USER_MEMORY_REGION2 should have failed, dirty logging private memory is unsupported");
+
+ r = __vm_set_user_memory_region2(vm, 0,
+ KVM_MEM_READONLY | KVM_MEM_GUEST_MEMFD,
+ 0, MEM_REGION_SIZE, NULL, guest_memfd, 0);
+ TEST_ASSERT(r && errno == EINVAL,
+ "KVM_SET_USER_MEMORY_REGION2 should have failed, read-only GUEST_MEMFD memslots are unsupported");
+
+ close(guest_memfd);
}
}
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 10bfc88a69f7..0f50960b0e3a 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1615,7 +1615,13 @@ static int check_memory_region_flags(struct kvm *kvm,
valid_flags &= ~KVM_MEM_LOG_DIRTY_PAGES;
#ifdef __KVM_HAVE_READONLY_MEM
- valid_flags |= KVM_MEM_READONLY;
+ /*
+ * GUEST_MEMFD is incompatible with read-only memslots, as writes to
+ * read-only memslots have emulated MMIO, not page fault, semantics,
+ * and KVM doesn't allow emulated MMIO for private memory.
+ */
+ if (!(mem->flags & KVM_MEM_GUEST_MEMFD))
+ valid_flags |= KVM_MEM_READONLY;
#endif
if (mem->flags & ~valid_flags)