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 <groug@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;
>       }
...