FAILED: patch "[PATCH] x86/xen: fix init of balloon stats again" failed to apply to 6.6-stable tree

PATCH New [email protected] 2 participants 3 messages Sep 3 – Sep 4

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Stable branch Xen hypervisor interface

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author maintainer

2026-09-03 12:47 UTC #0 lore raw

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 5d00a11d484e7b31a358cd81afebccb4602dbe8c
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026090359-kissable-animate-cb41@gregkh' --subject-prefix 'PATCH 6.6.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 5d00a11d484e7b31a358cd81afebccb4602dbe8c Mon Sep 17 00:00:00 2001
From: Roger Pau Monne <[email protected]>
Date: Wed, 5 Aug 2026 11:40:07 +0200
Subject: [PATCH] x86/xen: fix init of balloon stats again
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

The handling of extra memory regions done in balloon_add_regions() is not correct for PV guests, since the initial target is set to reflect the real memory the system has, not what's described on the memory map, which can be higher if memory != maxmem.

Introduce separate logic for addition vs subtraction in balloon_add_regions() and handle extra regions correctly by adding them to the total amount of pages, instead of subtracting from the current and target pages amounts.

In the common case PV domU/dom0 and PVH dom0 will use the addition path, since the initial target reflects the real assigned memory. HVM and PVH domUs use the subtraction path, since the target is set based on the amount of memory reported in the memory map, without accounting for released regions.

Fixes 87af633689ce ("x86/xen: fix balloon target initialization for PVH dom0")

Fixes 0949c646d646 ("Partial revert "x86/xen: fix balloon target initialization for PVH dom0"")

Signed-off-by Roger Pau Monné <[email protected]>

Cc [email protected]

Reviewed-by Juergen Gross <[email protected]>

Tested-by Matthias Goergens <[email protected]>

Signed-off-by Juergen Gross <[email protected]>

Message-ID: <[email protected]>

drivers/xen/balloon.c +19 ~~-10~~

index e7f1d4ca6d75..e7f74ea7cd5e 100644
@@ -679,7 +679,7 @@ void xen_free_ballooned_pages(unsigned int nr_pages, struct page **pages)
 }
 EXPORT_SYMBOL(xen_free_ballooned_pages);
 
-static int __init balloon_add_regions(void)
+static int __init balloon_add_regions(bool append)
 {
 	unsigned long start_pfn, pages;
 	unsigned long pfn, extra_pfn_end;

@@ -703,19 +703,26 @@ static int __init balloon_add_regions(void)
 			balloon_append(pfn_to_page(pfn));
 
 		/*
-		 * Extra regions are accounted for in the physmap, but need
-		 * decreasing from current_pages and target_pages to balloon
-		 * down the initial allocation, because they are already
-		 * accounted for in total_pages.
+		 * There are two different use-cases depending on how the
+		 * initial memory target is fetched.  For PVH dom0 and PV the
+		 * target is usually set to reflect the domain assigned memory,
+		 * and hence extra regions need adding.
+		 *
+		 * OTOH for HVM and PVH domU the target is set to the amount of
+		 * RAM reported in the memory map, and hence extra regions need
+		 * subtracting to reflect the real memory usage.
 		 */
 		pages = extra_pfn_end - start_pfn;
-		if (pages >= balloon_stats.current_pages ||
-		    pages >= balloon_stats.target_pages) {
+		if (append) {
+			balloon_stats.total_pages += pages;
+		} else if (pages >= balloon_stats.current_pages ||
+		           pages >= balloon_stats.target_pages) {
 			WARN(1, "Extra pages underflow current target");
 			return -ERANGE;
+		} else {
+			balloon_stats.current_pages -= pages;
+			balloon_stats.target_pages -= pages;
 		}
-		balloon_stats.current_pages -= pages;
-		balloon_stats.target_pages -= pages;
 	}
 
 	return 0;

@@ -726,6 +733,7 @@ static int __init balloon_init(void)
 	struct task_struct *task;
 	long current_pages = 0;
 	domid_t domid = DOMID_SELF;
+	bool append = true;
 	int rc;
 
 	if (!xen_domain())

@@ -745,6 +753,7 @@ static int __init balloon_init(void)
 		} else {
 			if (xen_unpopulated_pages >= get_num_physpages())
 				goto underflow;
+			append = false;
 			current_pages = get_num_physpages() -
 			                xen_unpopulated_pages;
 		}

@@ -767,7 +776,7 @@ static int __init balloon_init(void)
 	register_sysctl_init("xen/balloon", balloon_table);
 #endif
 
-	rc = balloon_add_regions();
+	rc = balloon_add_regions(append);
 	if (rc)
 		return rc;

Sasha Levin

maintainer

2026-09-04 11:02 UTC #1 lore raw

PATCH 1/2 xen/balloon: improve accuracy of initial balloon target for dom0

From: Roger Pau Monne <[email protected]>

[ Upstream commit b13cd24c15d74f6dfcddf0d53ae6efb58d3f0461 ]

The dom0 balloon target set by the toolstack is the value returned by XENMEM_current_reservation. Do the same in the kernel balloon driver and set the current allocation to the value returned by XENMEM_current_reservation. On my test system this causes the kernel balloon driver target to exactly match the value set by the toolstack in xenstore.

Note this approach can be used by both PV and PVH dom0s, as the toolstack always uses XENMEM_current_reservation to set the initial target regardless of the dom0 type.

Signed-off-by Roger Pau Monné <[email protected]>

Reviewed-by Juergen Gross <[email protected]>

Signed-off-by Juergen Gross <[email protected]>

Message-ID: <[email protected]>
Stable-dep-of: 5d00a11d484e ("x86/xen: fix init of balloon stats again")

Signed-off-by Sasha Levin <[email protected]>

---
 drivers/xen/balloon.c | 27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

drivers/xen/balloon.c +17 ~~-10~~

index a76d5530533ff..1fb5dbce0b66c 100644
@@ -716,7 +716,8 @@ static int __init balloon_add_regions(void)
 static int __init balloon_init(void)
 {
 	struct task_struct *task;
-	unsigned long current_pages;
+	long current_pages = 0;
+	domid_t domid = DOMID_SELF;
 	int rc;
 
 	if (!xen_domain())

@@ -724,15 +725,21 @@ static int __init balloon_init(void)
 
 	pr_info("Initialising balloon driver\n");
 
-	if (xen_pv_domain()) {
-		if (xen_released_pages >= xen_start_info->nr_pages)
-			goto underflow;
-		current_pages = min(xen_start_info->nr_pages -
-		                    xen_released_pages, max_pfn);
-	} else {
-		if (xen_unpopulated_pages >= get_num_physpages())
-			goto underflow;
-		current_pages = get_num_physpages() - xen_unpopulated_pages;
+	if (xen_initial_domain())
+		current_pages = HYPERVISOR_memory_op(XENMEM_current_reservation,
+		                                     &domid);
+	if (current_pages <= 0) {
+		if (xen_pv_domain()) {
+			if (xen_released_pages >= xen_start_info->nr_pages)
+				goto underflow;
+			current_pages = min(xen_start_info->nr_pages -
+			                    xen_released_pages, max_pfn);
+		} else {
+			if (xen_unpopulated_pages >= get_num_physpages())
+				goto underflow;
+			current_pages = get_num_physpages() -
+			                xen_unpopulated_pages;
+		}
 	}
 
 	balloon_stats.current_pages = current_pages;

Signature · 1 line

2.53.0

Sasha Levin

maintainer

2026-09-04 11:02 UTC #2 lore raw

PATCH 2/2 x86/xen: fix init of balloon stats again

From: Roger Pau Monne <[email protected]>

[ Upstream commit 5d00a11d484e7b31a358cd81afebccb4602dbe8c ]

Fixes 87af633689ce ("x86/xen: fix balloon target initialization for PVH dom0")

Fixes 0949c646d646 ("Partial revert "x86/xen: fix balloon target initialization for PVH dom0"")

Signed-off-by Roger Pau Monné <[email protected]>

Cc [email protected]

Reviewed-by Juergen Gross <[email protected]>

Tested-by Matthias Goergens <[email protected]>

Signed-off-by Juergen Gross <[email protected]>

Message-ID: <[email protected]>

Signed-off-by Sasha Levin <[email protected]>

---
 drivers/xen/balloon.c | 29 +++++++++++++++++++----------
 1 file changed, 19 insertions(+), 10 deletions(-)

drivers/xen/balloon.c +19 ~~-10~~

index 1fb5dbce0b66c..af34de2a8a23d 100644
@@ -671,7 +671,7 @@ void xen_free_ballooned_pages(unsigned int nr_pages, struct page **pages)
 }
 EXPORT_SYMBOL(xen_free_ballooned_pages);
 
-static int __init balloon_add_regions(void)
+static int __init balloon_add_regions(bool append)
 {
 	unsigned long start_pfn, pages;
 	unsigned long pfn, extra_pfn_end;

@@ -695,19 +695,26 @@ static int __init balloon_add_regions(void)
 			balloon_append(pfn_to_page(pfn));
 
 		/*
-		 * Extra regions are accounted for in the physmap, but need
-		 * decreasing from current_pages and target_pages to balloon
-		 * down the initial allocation, because they are already
-		 * accounted for in total_pages.
+		 * There are two different use-cases depending on how the
+		 * initial memory target is fetched.  For PVH dom0 and PV the
+		 * target is usually set to reflect the domain assigned memory,
+		 * and hence extra regions need adding.
+		 *
+		 * OTOH for HVM and PVH domU the target is set to the amount of
+		 * RAM reported in the memory map, and hence extra regions need
+		 * subtracting to reflect the real memory usage.
 		 */
 		pages = extra_pfn_end - start_pfn;
-		if (pages >= balloon_stats.current_pages ||
-		    pages >= balloon_stats.target_pages) {
+		if (append) {
+			balloon_stats.total_pages += pages;
+		} else if (pages >= balloon_stats.current_pages ||
+		           pages >= balloon_stats.target_pages) {
 			WARN(1, "Extra pages underflow current target");
 			return -ERANGE;
+		} else {
+			balloon_stats.current_pages -= pages;
+			balloon_stats.target_pages -= pages;
 		}
-		balloon_stats.current_pages -= pages;
-		balloon_stats.target_pages -= pages;
 	}
 
 	return 0;

@@ -718,6 +725,7 @@ static int __init balloon_init(void)
 	struct task_struct *task;
 	long current_pages = 0;
 	domid_t domid = DOMID_SELF;
+	bool append = true;
 	int rc;
 
 	if (!xen_domain())

@@ -737,6 +745,7 @@ static int __init balloon_init(void)
 		} else {
 			if (xen_unpopulated_pages >= get_num_physpages())
 				goto underflow;
+			append = false;
 			current_pages = get_num_physpages() -
 			                xen_unpopulated_pages;
 		}

@@ -759,7 +768,7 @@ static int __init balloon_init(void)
 	register_sysctl_init("xen/balloon", balloon_table);
 #endif
 
-	rc = balloon_add_regions();
+	rc = balloon_add_regions(append);
 	if (rc)
 		return rc;

Signature · 1 line

2.53.0