[RFC PATCH 22/67] KVM: Add per-VM flag to mark read-only memory as unsupported

From: isaku . yamahata
Date: Mon Nov 16 2020 - 13:32:45 EST


From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>

Add a flag for TDX to flag RO memory as unsupported and propagate it to
KVM_MEM_READONLY to allow reporting RO memory as unsupported on a per-VM
basis. TDX1 doesn't expose permission bits to the VMM in the SEPT
tables, i.e. doesn't support read-only private memory.

Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
Co-developed-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
---
arch/x86/kvm/x86.c | 4 +++-
include/linux/kvm_host.h | 4 ++++
virt/kvm/kvm_main.c | 8 +++++---
3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 01380f057d9f..4060f3d91f74 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3695,7 +3695,6 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
case KVM_CAP_ASYNC_PF_INT:
case KVM_CAP_GET_TSC_KHZ:
case KVM_CAP_KVMCLOCK_CTRL:
- case KVM_CAP_READONLY_MEM:
case KVM_CAP_HYPERV_TIME:
case KVM_CAP_IOAPIC_POLARITY_IGNORED:
case KVM_CAP_TSC_DEADLINE_TIMER:
@@ -3785,6 +3784,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
if (kvm_x86_ops.is_vm_type_supported(KVM_X86_TDX_VM))
r |= BIT(KVM_X86_TDX_VM);
break;
+ case KVM_CAP_READONLY_MEM:
+ r = kvm && kvm->readonly_mem_unsupported ? 0 : 1;
+ break;
default:
break;
}
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 95371750c23f..1a0df7b83fd0 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -517,6 +517,10 @@ struct kvm {
pid_t userspace_pid;
unsigned int max_halt_poll_ns;

+#ifdef __KVM_HAVE_READONLY_MEM
+ bool readonly_mem_unsupported;
+#endif
+
bool vm_bugged;
};

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 3dc41b6e12a0..572a66a61c29 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1100,12 +1100,14 @@ static void update_memslots(struct kvm_memslots *slots,
}
}

-static int check_memory_region_flags(const struct kvm_userspace_memory_region *mem)
+static int check_memory_region_flags(struct kvm *kvm,
+ const struct kvm_userspace_memory_region *mem)
{
u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;

#ifdef __KVM_HAVE_READONLY_MEM
- valid_flags |= KVM_MEM_READONLY;
+ if (!kvm->readonly_mem_unsupported)
+ valid_flags |= KVM_MEM_READONLY;
#endif

if (mem->flags & ~valid_flags)
@@ -1278,7 +1280,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
int as_id, id;
int r;

- r = check_memory_region_flags(mem);
+ r = check_memory_region_flags(kvm, mem);
if (r)
return r;

--
2.17.1