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Date:      Wed, 10 Jun 2026 04:01:16 +0000
From:      Kyle Evans <kevans@FreeBSD.org>
To:        src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org
Subject:   git: 92a2764ba175 - stable/15 - linuxkpi: work with numpages > 1 in the set_pages_*() KPIs
Message-ID:  <6a28e18c.258f5.2a285432@gitrepo.freebsd.org>
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The branch stable/15 has been updated by kevans:

URL: https://cgit.FreeBSD.org/src/commit/?id=92a2764ba175e5af550d96a4b509d7776c6dffa6

commit 92a2764ba175e5af550d96a4b509d7776c6dffa6
Author:     Kyle Evans <kevans@FreeBSD.org>
AuthorDate: 2026-05-19 03:22:21 +0000
Commit:     Kyle Evans <kevans@FreeBSD.org>
CommitDate: 2026-06-10 04:00:37 +0000

    linuxkpi: work with numpages > 1 in the set_pages_*() KPIs
    
    These calls are used for buddy pages at least in drm's ttm_pool, which
    leads to a panic when we invoke lowmem handlers and drm tries to shrink
    the pool.
    
    Cope with numpages > 1 by traversing the contiguous pages and executing
    the adjustment there, as well, as suggested by markj@.  Previous
    versions have tried to use the corresponding `set_memory_*()` functions,
    but it is believed that not updating `md.pat_mode` breaks subsequent
    userspace mappings in ways that may result in things like screen tearing
    or other artifacts when running i915kms.
    
    This stabilized my amdgpu laptop running two VMs, chromium and a
    concurrent buildworld.
    
    Reviewed by:    bz, markj
    
    (cherry picked from commit 67f7f2781daa9bd398b424ffe2bd0be67f37f03d)
    (cherry picked from commit 8dad29555a5807bf21941807752e1589e20312de)
---
 sys/compat/linuxkpi/common/include/asm/set_memory.h | 15 +++------------
 sys/compat/linuxkpi/common/include/linux/page.h     |  2 ++
 sys/compat/linuxkpi/common/src/linux_page.c         | 21 +++++++++++++++++++++
 3 files changed, 26 insertions(+), 12 deletions(-)

diff --git a/sys/compat/linuxkpi/common/include/asm/set_memory.h b/sys/compat/linuxkpi/common/include/asm/set_memory.h
index 1019aaf264a0..54a1311ef9a5 100644
--- a/sys/compat/linuxkpi/common/include/asm/set_memory.h
+++ b/sys/compat/linuxkpi/common/include/asm/set_memory.h
@@ -65,32 +65,23 @@ set_memory_wb(unsigned long addr, int numpages)
 static inline int
 set_pages_uc(struct page *page, int numpages)
 {
-	KASSERT(numpages == 1, ("%s: numpages %d", __func__, numpages));
-
-	pmap_page_set_memattr(page, VM_MEMATTR_UNCACHEABLE);
-	return (0);
+	return (lkpi_set_pages_attr(page, numpages, VM_MEMATTR_UNCACHEABLE));
 }
 
 static inline int
 set_pages_wc(struct page *page, int numpages)
 {
-	KASSERT(numpages == 1, ("%s: numpages %d", __func__, numpages));
-
 #ifdef VM_MEMATTR_WRITE_COMBINING
-	pmap_page_set_memattr(page, VM_MEMATTR_WRITE_COMBINING);
+	return (lkpi_set_pages_attr(page, numpages, VM_MEMATTR_WRITE_COMBINING));
 #else
 	return (set_pages_uc(page, numpages));
 #endif
-	return (0);
 }
 
 static inline int
 set_pages_wb(struct page *page, int numpages)
 {
-	KASSERT(numpages == 1, ("%s: numpages %d", __func__, numpages));
-
-	pmap_page_set_memattr(page, VM_MEMATTR_WRITE_BACK);
-	return (0);
+	return (lkpi_set_pages_attr(page, numpages, VM_MEMATTR_WRITE_BACK));
 }
 
 static inline int
diff --git a/sys/compat/linuxkpi/common/include/linux/page.h b/sys/compat/linuxkpi/common/include/linux/page.h
index 37ab593a64e9..6f5f37d2fd0f 100644
--- a/sys/compat/linuxkpi/common/include/linux/page.h
+++ b/sys/compat/linuxkpi/common/include/linux/page.h
@@ -127,4 +127,6 @@ clflush_cache_range(void *addr, unsigned int size)
 }
 #endif
 
+int lkpi_set_pages_attr(struct page *page, int numpages, vm_memattr_t ma);
+
 #endif	/* _LINUXKPI_LINUX_PAGE_H_ */
diff --git a/sys/compat/linuxkpi/common/src/linux_page.c b/sys/compat/linuxkpi/common/src/linux_page.c
index d8b65a12dc67..f562bd5e0dbd 100644
--- a/sys/compat/linuxkpi/common/src/linux_page.c
+++ b/sys/compat/linuxkpi/common/src/linux_page.c
@@ -710,6 +710,27 @@ lkpi_arch_phys_wc_del(int reg)
 #endif
 }
 
+int
+lkpi_set_pages_attr(struct page *page, int numpages, vm_memattr_t ma)
+{
+	while (numpages-- > 0) {
+		/*
+		 * pmap_page_set_memattr() would only update the DMAP mapping
+		 * if it's a normal page, leaving the kernel map untouched.
+		 */
+		MPASS(page->object != kernel_object);
+
+		/*
+		 * pmap_page_set_memattr() sets page->md.pat_mode, which is
+		 * crucial for future userspace mappings.
+		 */
+		pmap_page_set_memattr(page, ma);
+		page++;
+	}
+
+	return (0);
+}
+
 /*
  * This is a highly simplified version of the Linux page_frag_cache.
  * We only support up-to 1 single page as fragment size and we will
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