Re: [PATCH 4/4] spapr: Improve spapr_reallocate_hpt() error reporting

[Philippe Mathieu-Daudé]

On 10/26/20 1:40 PM, Greg Kurz wrote:

spapr_reallocate_hpt() has three users, two of which pass &error_fatal
and the third one, htab_load(), passes &local_err, uses it to detect
failures and simply propagates -EINVAL up to vmstate_load(), which will
cause QEMU to exit. It is thus confusing that spapr_reallocate_hpt()
doesn't return right away when an error is detected in some cases. Also,
the comment suggesting that the caller is welcome to try to carry on
seems like a remnant in this respect.

This can be improved:
- change spapr_reallocate_hpt() to always report a negative errno on
   failure, either as reported by KVM or -ENOSPC if the HPT is smaller
   than what was asked,
- use that to detect failures in htab_load() which is preferred over
   checking &local_err,
- propagate this negative errno to vmstate_load() because it is more
   accurate than propagating -EINVAL for all possible errors.

Signed-off-by: Greg Kurz <gr...@kaod.org>

...

-void spapr_reallocate_hpt(SpaprMachineState *spapr, int shift,
-                          Error **errp)
+int spapr_reallocate_hpt(SpaprMachineState *spapr, int shift, Error **errp)
  {
      ERRP_GUARD();
      long rc;
@@ -1496,7 +1495,7 @@ void spapr_reallocate_hpt(SpaprMachineState *spapr, int 
shift,

if (rc == -EOPNOTSUPP) {

          error_setg(errp, "HPT not supported in nested guests");
-        return;
+        return -EOPNOTSUPP;
      }

if (rc < 0) {

@@ -1504,8 +1503,7 @@ void spapr_reallocate_hpt(SpaprMachineState *spapr, int 
shift,
          error_setg_errno(errp, errno, "Failed to allocate KVM HPT of order 
%d",
                           shift);
          error_append_hint(errp, "Try smaller maxmem?\n");
-        /* This is almost certainly fatal, but if the caller really
-         * wants to carry on with shift == 0, it's welcome to try */
+        return -errno;

Maybe returning here should be in a previous patch.
Otherwise patch looks good.

      } else if (rc > 0) {
          /* kernel-side HPT allocated */
          if (rc != shift) {
@@ -1513,6 +1511,7 @@ void spapr_reallocate_hpt(SpaprMachineState *spapr, int 
shift,
                         "Requested order %d HPT, but kernel allocated order 
%ld",
                         shift, rc);
              error_append_hint(errp, "Try smaller maxmem?\n");
+            return -ENOSPC;
          }

spapr->htab_shift = shift;

@@ -1533,6 +1532,7 @@ void spapr_reallocate_hpt(SpaprMachineState *spapr, int 
shift,
      /* We're setting up a hash table, so that means we're not radix */
      spapr->patb_entry = 0;
      spapr_set_all_lpcrs(0, LPCR_HR | LPCR_UPRT);
+    return 0;
  }

void spapr_setup_hpt(SpaprMachineState *spapr)

@@ -2286,11 +2286,13 @@ static int htab_load(QEMUFile *f, void *opaque, int 
version_id)
      }

if (section_hdr) {

+        int ret;
+
          /* First section gives the htab size */
-        spapr_reallocate_hpt(spapr, section_hdr, &local_err);
-        if (local_err) {
+        ret = spapr_reallocate_hpt(spapr, section_hdr, &local_err);
+        if (ret < 0) {
              error_report_err(local_err);
-            return -EINVAL;
+            return ret;
          }
          return 0;
      }

...