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

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.

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;
 		pr_err("API is supported only with radix page tables\n");
 		return -ENOTSUPP;
 	}

-- 
2.26.3

Haren Myneni [off-list ref] 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?

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.

On Tue, 2023-03-07 at 20:55 -0600, Nathan Lynch wrote:

Haren Myneni [off-list ref] writes:

quoted

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?

Thanks for your suggestions, I will add more explanation in the
description.

Even if copy/paste is not enabled, pseries_vas_dlpar_cpu() just returns
0 which allows lparcfg_write() returns success - will not affect DLPAR
operation.

  if (pseries_vas_dlpar_cpu() != 0)
       retval = H_HARDWARE;

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

It should not affect for dedicated processor
mode. pseries_vas_notifier() is registered if copy/paste is enabled. 

if (!rc && copypaste_feat) {
                if (firmware_has_feature(FW_FEATURE_LPAR))
                        of_reconfig_notifier_register(&pseries_vas_nb);

quoted

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].f

eat,
 				      (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.

Correct my mistake.

Thanks
Haren