Re: [PATCH] powerpc/pseries/vas: Ignore VAS update for DLPAR if copy/paste is not enabled

[Nathan Lynch <nathanl@linux.ibm.com>]

Haren Myneni <haren@linux.ibm.com> writes:
> The hypervisor supports user-mode NX from Power10. pseries_vas_dlpar_cpu()
> is called from lparcfg_write() to update VAS windows for DLPAR CPU event
> and the kernel gets -ENOTSUPP for HCALLs if the user-mode NX is not
> supported.

The commit text would be improved by more explanation about the higher
level failure mode here. Does lparcfg_write() fail when it shouldn't? If
so, does that cause a processor DLPAR operation to spuriously fail?

pseries_vas_dlpar_cpu() is also called from pseries_vas_notifier() in
dedicated processor mode. Does this problem affect that scenario also?

> This patch ignores updating VAS capabilities and returns success if the
> copy/paste feature is not enabled.
>
> Fixes: 2147783d6bf0 ("powerpc/pseries: Use lparcfg to reconfig VAS windows for DLPAR CPU")
> Signed-off-by: Haren Myneni <haren@linux.ibm.com>
> ---
>  arch/powerpc/platforms/pseries/vas.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/arch/powerpc/platforms/pseries/vas.c b/arch/powerpc/platforms/pseries/vas.c
> index 559112312810..dc003849d2c5 100644
> --- a/arch/powerpc/platforms/pseries/vas.c
> +++ b/arch/powerpc/platforms/pseries/vas.c
> @@ -856,6 +856,13 @@ int pseries_vas_dlpar_cpu(void)
>  {
>  	int new_nr_creds, rc;
>  
> +	/*
> +	 * NX-GZIP is not enabled. Nothing to do for DLPAR event
> +	 */
> +	if (!copypaste_feat)
> +		return 0;
> +
> +
>  	rc = h_query_vas_capabilities(H_QUERY_VAS_CAPABILITIES,
>  				      vascaps[VAS_GZIP_DEF_FEAT_TYPE].feat,
>  				      (u64)virt_to_phys(&hv_cop_caps));
> @@ -1012,6 +1019,7 @@ static int __init pseries_vas_init(void)
>  	 * Linux supports user space COPY/PASTE only with Radix
>  	 */
>  	if (!radix_enabled()) {
> +		copypaste_feat = 0;

copypaste_feat is a bool, so use false, not 0. But otherwise I think
this looks correct and consistent with the rest of the code in vas.c.