[PATCH v2 2/2] KVM: TDX: Return EINVAL, not EOPNOTSUPP, for NULL INIT_MEM_REGION source

[Sean Christopherson]

Return EINVAL instead of EOPNOTSUPP if userspace attempts to pass a NULL
pointer for the source page of INIT_MEM_REGION, so that KVM's ABI is
consistent between TDX and SNP (for LAUNCH_UPDATE).  EOPNOTSUPP was chosen
to be a forward-looking error code for when guest_memfd supports in-place
conversion, but even when in-place conversion comes along, it's an awkward
error code as KVM is deliberately choosing to disallow virtual address '0',
which is technically a legal userspace address.  I.e. it's not so much a
lack of support as it is that KVM reserves address '0' to simplify KVM's
internal implementation.

Opportunistically move the check so that it's co-located with the other
checks on the userspace address, and so that it's more obvious that a NULL
source address is explicitly disallowed.

Fixes: 2a62345b3052 ("KVM: guest_memfd: GUP source pages prior to populating guest memory")
Cc: Yan Zhao <yan.y.zhao@xxxxxxxxx>
Cc: Ackerley Tng <ackerleytng@xxxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/kvm/vmx/tdx.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index ffe9d0db58c5..b0ec054732b9 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -3198,9 +3198,6 @@ static int tdx_gmem_post_populate(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn,
 	if (KVM_BUG_ON(kvm_tdx->page_add_src, kvm))
 		return -EIO;
 
-	if (!src_page)
-		return -EOPNOTSUPP;
-
 	kvm_tdx->page_add_src = src_page;
 	ret = kvm_tdp_mmu_map_private_pfn(arg->vcpu, gfn, pfn);
 	kvm_tdx->page_add_src = NULL;
@@ -3247,8 +3244,8 @@ static int tdx_vcpu_init_mem_region(struct kvm_vcpu *vcpu, struct kvm_tdx_cmd *c
 	if (copy_from_user(&region, u64_to_user_ptr(cmd->data), sizeof(region)))
 		return -EFAULT;
 
-	if (!PAGE_ALIGNED(region.source_addr) || !PAGE_ALIGNED(region.gpa) ||
-	    !region.nr_pages ||
+	if (!PAGE_ALIGNED(region.source_addr) || !region.source_addr ||
+	    !PAGE_ALIGNED(region.gpa) || !region.nr_pages ||
 	    region.gpa + (region.nr_pages << PAGE_SHIFT) <= region.gpa ||
 	    !vt_is_tdx_private_gpa(kvm, region.gpa) ||
 	    !vt_is_tdx_private_gpa(kvm, region.gpa + (region.nr_pages << PAGE_SHIFT) - 1))
-- 
2.55.0.rc0.799.gd6f94ed593-goog