On Mon, 2022-02-14 at 13:08 +1000, Nicholas Piggin wrote:

Excerpts from Haren Myneni's message of January 22, 2022 5:56 am:

quoted

VAS windows can be closed in the hypervisor due to lost credits
when the core is removed. If these credits are available later
for core add, reopen these windows and set them active. When the
kernel sees page fault on the paste address, it creates new mapping
on the new paste address. Then the user space can continue to use
these windows and send HW compression requests to NX successfully.

Any reason to put this before the close windows patch? It would be
more logical to put it afterwards AFAIKS.

reconfig_open_windows() is just to reopen and set the status flag when
windows are closed. I thought adding handler first before closing /
unmap helps during git bisect. 

I can change. 

quoted

Signed-off-by: Haren Myneni <haren@linux.ibm.com>
---
 arch/powerpc/include/asm/vas.h          |  16 +++
 arch/powerpc/platforms/book3s/vas-api.c |   1 +
 arch/powerpc/platforms/pseries/vas.c    | 144
++++++++++++++++++++++++
 arch/powerpc/platforms/pseries/vas.h    |   8 +-
 4 files changed, 163 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/include/asm/vas.h

b/arch/powerpc/include/asm/vas.h
index 57573d9c1e09..f1efe86563cc 100644

--- a/arch/powerpc/include/asm/vas.h
+++ b/arch/powerpc/include/asm/vas.h

@@ -29,6 +29,19 @@
 #define VAS_THRESH_FIFO_GT_QTR_FULL	2
 #define VAS_THRESH_FIFO_GT_EIGHTH_FULL	3
 
+/*
+ * VAS window status
+ */
+#define VAS_WIN_ACTIVE		0x0	/* Used in platform

independent */
+					/* vas mmap() */
+/* The hypervisor returns these values */
+#define VAS_WIN_CLOSED		0x00000001
+#define VAS_WIN_INACTIVE	0x00000002 /* Inactive due to HW
failure */
+#define VAS_WIN_MOD_IN_PROCESS	0x00000003 /* Process of being
modified, */

While you're moving these and adding a comment, it would be good to 
list what hcalls they are relevant to. H_QUERY_VAS_WINDOW (which is
not
used anywhere yet?) These are also a 1-byte field, so '0x00', '0x01'
etc
would be more appropriate.

Yes, these status bits are assigned by the hypervisor and we are not
using / supporting them right now. I just list them as defined in PAPR
NX HCALLs.

For example: OS can modify the existing window with modify HCALL when
the window is used. During this time, the hypervisor return this status
with window query HCALL. 
 

quoted

+					   /* deallocated, or quiesced
*/
+/* Linux status bits */
+#define VAS_WIN_NO_CRED_CLOSE	0x00000004 /* Window is closed
due to */
+					   /* lost credit */

This is mixing a user defined bit field with hcall API value field.
You
also AFAIKS as yet don't fill in the hypervisor status anywhere.

I would make this it's own field entirely. A boolean would be nice,
if
possible.

Yes, HV status bits are not used here. 

In case if the window status is reported thorugh sysfs in future,
thought that it will be simpler to have one status flag. 

I can add 'hv_status' for the hypervisor status flag in pseries_vas-
window struct and 'status' for linux in vas_window struct. 

We also need one more status for migration. So boolean may not be used.

quoted

 /*
  * Get/Set bit fields
  */

@@ -59,6 +72,8 @@ struct vas_user_win_ref {
 	struct pid *pid;	/* PID of owner */
 	struct pid *tgid;	/* Thread group ID of owner */
 	struct mm_struct *mm;	/* Linux process mm_struct */
+	struct mutex mmap_mutex;	/* protects paste address mmap() */
+					/* with DLPAR close/open

windows */
 };
 
 /*

@@ -67,6 +82,7 @@ struct vas_user_win_ref {
 struct vas_window {
 	u32 winid;
 	u32 wcreds_max;	/* Window credits */
+	u32 status;
 	enum vas_cop_type cop;
 	struct vas_user_win_ref task_ref;
 	char *dbgname;

diff --git a/arch/powerpc/platforms/book3s/vas-api.c

b/arch/powerpc/platforms/book3s/vas-api.c
index 4d82c92ddd52..2b0ced611f32 100644

--- a/arch/powerpc/platforms/book3s/vas-api.c
+++ b/arch/powerpc/platforms/book3s/vas-api.c

@@ -316,6 +316,7 @@ static int coproc_ioc_tx_win_open(struct file

*fp, unsigned long arg)
 		return PTR_ERR(txwin);
 	}
 
+	mutex_init(&txwin->task_ref.mmap_mutex);
 	cp_inst->txwin = txwin;
 
 	return 0;

diff --git a/arch/powerpc/platforms/pseries/vas.c

b/arch/powerpc/platforms/pseries/vas.c
index 2ef56157634f..d9ff73d7704d 100644

--- a/arch/powerpc/platforms/pseries/vas.c
+++ b/arch/powerpc/platforms/pseries/vas.c

@@ -501,6 +501,7 @@ static int __init get_vas_capabilities(u8 feat,

enum vas_cop_feat_type type,
 	memset(vcaps, 0, sizeof(*vcaps));
 	INIT_LIST_HEAD(&vcaps->list);
 
+	vcaps->feat = feat;
 	caps = &vcaps->caps;
 
 	rc = h_query_vas_capabilities(H_QUERY_VAS_CAPABILITIES, feat,

@@ -539,6 +540,145 @@ static int __init get_vas_capabilities(u8

feat, enum vas_cop_feat_type type,
 	return 0;
 }
 
+/*
+ * VAS windows can be closed due to lost credits when the core is
+ * removed. So reopen them if credits are available due to DLPAR
+ * core add and set the window active status. When NX sees the
page
+ * fault on the unmapped paste address, the kernel handles the
fault
+ * by setting the remapping to new paste address if the window is
+ * active.
+ */
+static int reconfig_open_windows(struct vas_caps *vcaps, int
creds)
+{
+	long domain[PLPAR_HCALL9_BUFSIZE] = {VAS_DEFAULT_DOMAIN_ID};
+	struct vas_cop_feat_caps *caps = &vcaps->caps;
+	struct pseries_vas_window *win = NULL, *tmp;
+	int rc, mv_ents = 0;
+
+	/*
+	 * Nothing to do if there are no closed windows.
+	 */
+	if (!vcaps->close_wins)
+		return 0;
+
+	/*
+	 * For the core removal, the hypervisor reduces the credits
+	 * assigned to the LPAR and the kernel closes VAS windows
+	 * in the hypervisor depends on reduced credits. The kernel
+	 * uses LIFO (the last windows that are opened will be closed
+	 * first) and expects to open in the same order when credits
+	 * are available.
+	 * For example, 40 windows are closed when the LPAR lost 2
cores
+	 * (dedicated). If 1 core is added, this LPAR can have 20 more
+	 * credits. It means the kernel can reopen 20 windows. So move
+	 * 20 entries in the VAS windows lost and reopen next 20
windows.
+	 */
+	if (vcaps->close_wins > creds)
+		mv_ents = vcaps->close_wins - creds;
+
+	list_for_each_entry_safe(win, tmp, &vcaps->list, win_list) {
+		if (!mv_ents)
+			break;
+
+		mv_ents--;
+	}
+
+	list_for_each_entry_safe_from(win, tmp, &vcaps->list, win_list)
{
+		/*
+		 * Nothing to do on this window if it is not closed
+		 * with VAS_WIN_NO_CRED_CLOSE
+		 */
+		if (!(win->vas_win.status & VAS_WIN_NO_CRED_CLOSE))
+			continue;
+
+		rc = allocate_setup_window(win, (u64 *)&domain[0],
+					   caps->win_type);
+		if (rc)
+			return rc;
+
+		rc = h_modify_vas_window(win);
+		if (rc)
+			goto out;
+
+		mutex_lock(&win->vas_win.task_ref.mmap_mutex);
+		/*
+		 * Set window status to active
+		 */
+		win->vas_win.status &= ~VAS_WIN_NO_CRED_CLOSE;
+		mutex_unlock(&win->vas_win.task_ref.mmap_mutex);

What's the mutex protecting? If status can change, what happens if
it 
changed between checking it above and this point?

We need this mutex to protect status flag between
reconfig_close/open_windows() and VAS mmap handler. 
 We hold pseries_mutex() before calling recnfig_close/popen_windows(),
so not an issue here.

quoted

+		win->win_type = caps->win_type;
+		if (!--vcaps->close_wins)
+			break;
+	}
+
+	return 0;
+out:
+	/*
+	 * Window modify HCALL failed. So close the window to the
+	 * hypervisor and return.
+	 */
+	free_irq_setup(win);
+	h_deallocate_vas_window(win->vas_win.winid);
+	return rc;
+}
+
+/*
+ * Get new VAS capabilities when the core add/removal
configuration
+ * changes. Reconfig window configurations based on the credits
+ * availability from this new capabilities.
+ */
+static int vas_reconfig_capabilties(u8 type)
+{
+	struct hv_vas_cop_feat_caps *hv_caps;
+	struct vas_cop_feat_caps *caps;
+	int lpar_creds, new_creds;
+	struct vas_caps *vcaps;
+	int rc = 0;
+
+	if (type >= VAS_MAX_FEAT_TYPE) {
+		pr_err("Invalid credit type %d\n", type);
+		return -EINVAL;
+	}
+
+	vcaps = &vascaps[type];
+	caps = &vcaps->caps;
+
+	hv_caps = kmalloc(sizeof(*hv_caps), GFP_KERNEL);
+	if (!hv_caps)
+		return -ENOMEM;
+
+	mutex_lock(&vas_pseries_mutex);
+	rc = h_query_vas_capabilities(H_QUERY_VAS_CAPABILITIES, vcaps-

quoted

feat,

+				      (u64)virt_to_phys(hv_caps));
+	if (rc)
+		goto out;
+
+	new_creds = be16_to_cpu(hv_caps->target_lpar_creds);
+
+	lpar_creds = atomic_read(&caps->target_creds);

NBD but it would be slightly clearer that new_creds is the absolute 
value not the number of new credits if you call these two
new_nr_creds and old_nr_creds or prev_nr_creds.

Sure will change.

quoted

+
+	atomic_set(&caps->target_creds, new_creds);
+	/*
+	 * The total number of available credits may be decreased or
+	 * inceased with DLPAR operation. Means some windows have to be
+	 * closed / reopened. Hold the vas_pseries_mutex so that the
+	 * the user space can not open new windows.
+	 */
+	if (lpar_creds <  new_creds) {
+		/*
+		 * If the existing target credits is less than the new
+		 * target, reopen windows if they are closed due to
+		 * the previous DLPAR (core removal).
+		 */
+		rc = reconfig_open_windows(vcaps, new_creds -
lpar_creds);
+	}
+
+out:
+	mutex_unlock(&vas_pseries_mutex);
+	kfree(hv_caps);
+	return rc;
+}
+
 /*
  * Total number of default credits available (target_credits)
  * in LPAR depends on number of cores configured. It varies based
on

@@ -565,6 +705,10 @@ static int pseries_vas_notifier(struct

notifier_block *nb,
 	if (!intserv)
 		return NOTIFY_OK;
 
+	rc = vas_reconfig_capabilties(VAS_GZIP_DEF_FEAT_TYPE);
+	if (rc)
+		pr_err("Failed reconfig VAS capabilities with
DLPAR\n");
+
 	return rc;
 }
 

diff --git a/arch/powerpc/platforms/pseries/vas.h

b/arch/powerpc/platforms/pseries/vas.h
index 0538760d13be..45b62565955b 100644

--- a/arch/powerpc/platforms/pseries/vas.h
+++ b/arch/powerpc/platforms/pseries/vas.h

@@ -21,12 +21,6 @@
 #define VAS_MOD_WIN_FLAGS	(VAS_MOD_WIN_JOBS_KILL | VAS_MOD_WIN_DR

| \
 				VAS_MOD_WIN_PR | VAS_MOD_WIN_SF)
 
-#define VAS_WIN_ACTIVE		0x0
-#define VAS_WIN_CLOSED		0x1
-#define VAS_WIN_INACTIVE	0x2	/* Inactive due to HW failure */
-/* Process of being modified, deallocated, or quiesced */
-#define VAS_WIN_MOD_IN_PROCESS	0x3
-
 #define VAS_COPY_PASTE_USER_MODE	0x00000001
 #define VAS_COP_OP_USER_MODE		0x00000010
 

@@ -84,6 +78,8 @@ struct vas_cop_feat_caps {
 struct vas_caps {
 	struct vas_cop_feat_caps caps;
 	struct list_head list;	/* List of open windows */
+	int close_wins;		/* closed windows in the hypervisor

for DLPAR */

'nr_closed_wins'

This does not look like a capability. Although I guess neither do
some
of the fields (used_creds) in vas_cop_feat_caps. Why not at least put
this there with the rest of those credits fields?

We can add used_credits() here since it is not part of HV capability.
It was included in previous pathes, So I did not change, 

Thanks
Haren

Thanks,
Nick

quoted

+	u8 feat;		/* Feature type */
 };
 
 /*
-- 
2.27.0