KVM: SEV: Pin guest memory for write for RECEIVE_UPDATE_DATA

Require the target guest page to be writable when pinning memory for
RECEIVE_UPDATE_DATA.  Per the SEV API, the PSP writes to guest memory:

  The result is then encrypted with GCTX.VEK and written to the memory
  pointed to by GUEST_PADDR field.

Fixes: 15fb7de ("KVM: SVM: Add KVM_SEV_RECEIVE_UPDATE_DATA command")
Cc: [email protected]
Cc: Peter Gonda <[email protected]>
Cc: Marc Orr <[email protected]>
Cc: Tom Lendacky <[email protected]>
Cc: Brijesh Singh <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
Message-Id: <[email protected]>
Reviewed-by: Brijesh Singh <[email protected]>
Reviewed-by: Peter Gonda <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>

arch/x86/kvm/svm/sev.c

@@ -1473,7 +1473,7 @@ static int sev_receive_update_data(struct kvm *kvm, struct kvm_sev_cmd *argp)
 
 	/* Pin guest memory */
 	guest_page = sev_pin_memory(kvm, params.guest_uaddr & PAGE_MASK,
-				    PAGE_SIZE, &n, 0);
+				    PAGE_SIZE, &n, 1);
 	if (IS_ERR(guest_page)) {
 		ret = PTR_ERR(guest_page);
 		goto e_free_trans;