chore(hiding_ci): add userfault Linux patches

Include the following patch series rebased on top of the v7 of "KVM:
Mapping guest_memfd backed memory at the host for software protected
VMs"
(https://<lor>/kvm/20250318161823.4005529-1-tabba@google.com/, replace
"<lor>" with "lore.kernel.org" in this and the following links):
 - v4 "Direct Map Removal for guest_memfd"
   (https://<lor>/kvm/20250221160728.1584559-1-roypat@amazon.co.uk/),
   with fixups
 - v2 "KVM: Introduce KVM Userfault"
   (https://<lor>/kvm/20250109204929.1106563-1-jthoughton@google.com/)
 - v3 "KVM: guest_memfd: use write for population"
   (https://<lor>/kvm/20250303130838.28812-1-kalyazin@amazon.com/)
 - v3 "KVM: guest_memfd: support for uffd minor"
   (https://<lor>/kvm/20250404154352.23078-1-kalyazin@amazon.com/),
   with fixups

After this change all patches are represented as plain text files,
meaning no patches are required to be fetched via a lore link.

Signed-off-by: Nikita Kalyazin <kalyazin@amazon.com>

Author: kalyazin

resources/hiding_ci/patches/0001-mm-Consolidate-freeing-of-typed-folios-on-final-foli.patch

@@ -0,0 +1,109 @@
+From f9ca710b51263ce8317cc2fa02232e456fa1f39c Mon Sep 17 00:00:00 2001
+From: Fuad Tabba <tabba@google.com>
+Date: Tue, 18 Mar 2025 16:18:15 +0000
+Subject: [PATCH 01/34] mm: Consolidate freeing of typed folios on final
+ folio_put()
+
+Some folio types, such as hugetlb, handle freeing their own
+folios. Moreover, guest_memfd will require being notified once a
+folio's reference count reaches 0 to facilitate shared to private
+folio conversion, without the folio actually being freed at that
+point.
+
+As a first step towards that, this patch consolidates freeing
+folios that have a type. The first user is hugetlb folios. Later
+in this patch series, guest_memfd will become the second user of
+this.
+
+Suggested-by: David Hildenbrand <david@redhat.com>
+Acked-by: Vlastimil Babka <vbabka@suse.cz>
+Acked-by: David Hildenbrand <david@redhat.com>
+Signed-off-by: Fuad Tabba <tabba@google.com>
+---
+ include/linux/page-flags.h | 15 +++++++++++++++
+ mm/swap.c                  | 23 ++++++++++++++++++-----
+ 2 files changed, 33 insertions(+), 5 deletions(-)
+
+diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
+index 36d283552f80..6dc2494bd002 100644
+--- a/include/linux/page-flags.h
++++ b/include/linux/page-flags.h
+@@ -953,6 +953,21 @@ static inline bool page_has_type(const struct page *page)
+ 	return page_mapcount_is_type(data_race(page->page_type));
+ }
+ 
++static inline int page_get_type(const struct page *page)
++{
++	return page->page_type >> 24;
++}
++
++static inline bool folio_has_type(const struct folio *folio)
++{
++	return page_has_type(&folio->page);
++}
++
++static inline int folio_get_type(const struct folio *folio)
++{
++	return page_get_type(&folio->page);
++}
++
+ #define FOLIO_TYPE_OPS(lname, fname)					\
+ static __always_inline bool folio_test_##fname(const struct folio *folio) \
+ {									\
+diff --git a/mm/swap.c b/mm/swap.c
+index fc8281ef4241..47bc1bb919cc 100644
+--- a/mm/swap.c
++++ b/mm/swap.c
+@@ -94,6 +94,19 @@ static void page_cache_release(struct folio *folio)
+ 		unlock_page_lruvec_irqrestore(lruvec, flags);
+ }
+ 
++static void free_typed_folio(struct folio *folio)
++{
++	switch (folio_get_type(folio)) {
++#ifdef CONFIG_HUGETLBFS
++	case PGTY_hugetlb:
++		free_huge_folio(folio);
++		return;
++#endif
++	default:
++		WARN_ON_ONCE(1);
++	}
++}
++
+ void __folio_put(struct folio *folio)
+ {
+ 	if (unlikely(folio_is_zone_device(folio))) {
+@@ -101,8 +114,8 @@ void __folio_put(struct folio *folio)
+ 		return;
+ 	}
+ 
+-	if (folio_test_hugetlb(folio)) {
+-		free_huge_folio(folio);
++	if (unlikely(folio_has_type(folio))) {
++		free_typed_folio(folio);
+ 		return;
+ 	}
+ 
+@@ -966,13 +979,13 @@ void folios_put_refs(struct folio_batch *folios, unsigned int *refs)
+ 		if (!folio_ref_sub_and_test(folio, nr_refs))
+ 			continue;
+ 
+-		/* hugetlb has its own memcg */
+-		if (folio_test_hugetlb(folio)) {
++		if (unlikely(folio_has_type(folio))) {
++			/* typed folios have their own memcg, if any */
+ 			if (lruvec) {
+ 				unlock_page_lruvec_irqrestore(lruvec, flags);
+ 				lruvec = NULL;
+ 			}
+-			free_huge_folio(folio);
++			free_typed_folio(folio);
+ 			continue;
+ 		}
+ 		folio_unqueue_deferred_split(folio);
+
+base-commit: 4701f33a10702d5fc577c32434eb62adde0a1ae1
+-- 
+2.47.1
+

resources/hiding_ci/patches/0001.lore

@@ -0,0 +1,182 @@
+From 9a4d7cd855d14e1522f363e3e04ebb9fa0a90ff0 Mon Sep 17 00:00:00 2001
+From: Fuad Tabba <tabba@google.com>
+Date: Tue, 18 Mar 2025 16:18:16 +0000
+Subject: [PATCH 02/34] KVM: guest_memfd: Handle final folio_put() of
+ guest_memfd pages
+
+Before transitioning a guest_memfd folio to unshared, thereby
+disallowing access by the host and allowing the hypervisor to
+transition its view of the guest page as private, we need to be
+sure that the host doesn't have any references to the folio.
+
+This patch introduces a new type for guest_memfd folios, which
+isn't activated in this series but is here as a placeholder and
+to facilitate the code in the subsequent patch series. This will
+be used in the future to register a callback that informs the
+guest_memfd subsystem when the last reference is dropped,
+therefore knowing that the host doesn't have any remaining
+references.
+
+This patch also introduces the configuration option,
+KVM_GMEM_SHARED_MEM, which toggles support for mapping
+guest_memfd shared memory at the host.
+
+Signed-off-by: Fuad Tabba <tabba@google.com>
+Acked-by: Vlastimil Babka <vbabka@suse.cz>
+Acked-by: David Hildenbrand <david@redhat.com>
+---
+ include/linux/kvm_host.h   |  4 ++++
+ include/linux/page-flags.h | 16 ++++++++++++++++
+ mm/debug.c                 |  1 +
+ mm/swap.c                  | 29 +++++++++++++++++++++++++++++
+ virt/kvm/Kconfig           |  4 ++++
+ virt/kvm/guest_memfd.c     |  8 ++++++++
+ 6 files changed, 62 insertions(+)
+
+diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
+index f34f4cfaa513..3ad0719bfc4f 100644
+--- a/include/linux/kvm_host.h
++++ b/include/linux/kvm_host.h
+@@ -2571,4 +2571,8 @@ long kvm_arch_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu,
+ 				    struct kvm_pre_fault_memory *range);
+ #endif
+ 
++#ifdef CONFIG_KVM_GMEM_SHARED_MEM
++void kvm_gmem_handle_folio_put(struct folio *folio);
++#endif
++
+ #endif
+diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
+index 6dc2494bd002..daeee9a38e4c 100644
+--- a/include/linux/page-flags.h
++++ b/include/linux/page-flags.h
+@@ -933,6 +933,7 @@ enum pagetype {
+ 	PGTY_slab	= 0xf5,
+ 	PGTY_zsmalloc	= 0xf6,
+ 	PGTY_unaccepted	= 0xf7,
++	PGTY_guestmem	= 0xf8,
+ 
+ 	PGTY_mapcount_underflow = 0xff
+ };
+@@ -1082,6 +1083,21 @@ FOLIO_TYPE_OPS(hugetlb, hugetlb)
+ FOLIO_TEST_FLAG_FALSE(hugetlb)
+ #endif
+ 
++/*
++ * guestmem folios are used to back VM memory as managed by guest_memfd. Once
++ * the last reference is put, instead of freeing these folios back to the page
++ * allocator, they are returned to guest_memfd.
++ *
++ * For now, guestmem will only be set on these folios as long as they  cannot be
++ * mapped to user space ("private state"), with the plan of always setting that
++ * type once typed folios can be mapped to user space cleanly.
++ */
++#ifdef CONFIG_KVM_GMEM_SHARED_MEM
++FOLIO_TYPE_OPS(guestmem, guestmem)
++#else
++FOLIO_TEST_FLAG_FALSE(guestmem)
++#endif
++
+ PAGE_TYPE_OPS(Zsmalloc, zsmalloc, zsmalloc)
+ 
+ /*
+diff --git a/mm/debug.c b/mm/debug.c
+index 8d2acf432385..08bc42c6cba8 100644
+--- a/mm/debug.c
++++ b/mm/debug.c
+@@ -56,6 +56,7 @@ static const char *page_type_names[] = {
+ 	DEF_PAGETYPE_NAME(table),
+ 	DEF_PAGETYPE_NAME(buddy),
+ 	DEF_PAGETYPE_NAME(unaccepted),
++	DEF_PAGETYPE_NAME(guestmem),
+ };
+ 
+ static const char *page_type_name(unsigned int page_type)
+diff --git a/mm/swap.c b/mm/swap.c
+index 47bc1bb919cc..d8fda3948684 100644
+--- a/mm/swap.c
++++ b/mm/swap.c
+@@ -38,6 +38,10 @@
+ #include <linux/local_lock.h>
+ #include <linux/buffer_head.h>
+ 
++#ifdef CONFIG_KVM_GMEM_SHARED_MEM
++#include <linux/kvm_host.h>
++#endif
++
+ #include "internal.h"
+ 
+ #define CREATE_TRACE_POINTS
+@@ -94,6 +98,26 @@ static void page_cache_release(struct folio *folio)
+ 		unlock_page_lruvec_irqrestore(lruvec, flags);
+ }
+ 
++#ifdef CONFIG_KVM_GMEM_SHARED_MEM
++static void gmem_folio_put(struct folio *folio)
++{
++	/*
++	 * Perform the callback only as long as the KVM module is still loaded.
++	 * As long as the folio mapping is set, the folio is associated with a
++	 * guest_memfd inode.
++	 */
++	if (folio->mapping)
++		kvm_gmem_handle_folio_put(folio);
++
++	/*
++	 * If there are no references to the folio left, it's not associated
++	 * with a guest_memfd inode anymore.
++	 */
++	if (folio_ref_count(folio) == 0)
++		__folio_put(folio);
++}
++#endif /* CONFIG_KVM_GMEM_SHARED_MEM */
++
+ static void free_typed_folio(struct folio *folio)
+ {
+ 	switch (folio_get_type(folio)) {
+@@ -101,6 +125,11 @@ static void free_typed_folio(struct folio *folio)
+ 	case PGTY_hugetlb:
+ 		free_huge_folio(folio);
+ 		return;
++#endif
++#ifdef CONFIG_KVM_GMEM_SHARED_MEM
++	case PGTY_guestmem:
++		gmem_folio_put(folio);
++		return;
+ #endif
+ 	default:
+ 		WARN_ON_ONCE(1);
+diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
+index 54e959e7d68f..4e759e8020c5 100644
+--- a/virt/kvm/Kconfig
++++ b/virt/kvm/Kconfig
+@@ -124,3 +124,7 @@ config HAVE_KVM_ARCH_GMEM_PREPARE
+ config HAVE_KVM_ARCH_GMEM_INVALIDATE
+        bool
+        depends on KVM_PRIVATE_MEM
++
++config KVM_GMEM_SHARED_MEM
++       select KVM_PRIVATE_MEM
++       bool
+diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
+index b2aa6bf24d3a..5fc414becae5 100644
+--- a/virt/kvm/guest_memfd.c
++++ b/virt/kvm/guest_memfd.c
+@@ -13,6 +13,14 @@ struct kvm_gmem {
+ 	struct list_head entry;
+ };
+ 
++#ifdef CONFIG_KVM_GMEM_SHARED_MEM
++void kvm_gmem_handle_folio_put(struct folio *folio)
++{
++	WARN_ONCE(1, "A placeholder that shouldn't trigger. Work in progress.");
++}
++EXPORT_SYMBOL_GPL(kvm_gmem_handle_folio_put);
++#endif /* CONFIG_KVM_GMEM_SHARED_MEM */
++
+ /**
+  * folio_file_pfn - like folio_file_page, but return a pfn.
+  * @folio: The folio which contains this index.
+-- 
+2.47.1
+