[PATCH v6 0/9] populate/unpopulate memory when domain on static allocation

[PATCH v6 0/9] populate/unpopulate memory when domain on static allocation

[Penny Zheng]

Today when a domain unpopulates the memory on runtime, they will always
hand the memory over to the heap allocator. And it will be a problem if it
is a static domain.
Pages used as guest RAM for static domain shall always be reserved to this
domain only, and not be used for any other purposes, so they shall never go
back to heap allocator.

This patch serie intends to fix this issue, by adding pages on the new list
resv_page_list after having taken them off the "normal" list, when unpopulating
memory, and retrieving pages from resv page list(resv_page_list) when
populating memory.

---
v6 changes:
- rename PGC_staticmem to PGC_static
- remove #ifdef aroud function declaration
- use domain instead of sub-systems
- move non-zero is_domain_using_staticmem() from ARM header to common
header
- move PGC_static !CONFIG_STATIC_MEMORY definition to common header
- drop the lock before returning
---
v5 changes:
- introduce three new commits
- In order to avoid stub functions, we #define PGC_staticmem to non-zero only
when CONFIG_STATIC_MEMORY
- use "unlikely()" around pg->count_info & PGC_staticmem
- remove pointless "if", since mark_page_free() is going to set count_info
to PGC_state_free and by consequence clear PGC_staticmem
- move #define PGC_staticmem 0 to mm.h
- guard "is_domain_using_staticmem" under CONFIG_STATIC_MEMORY
- #define is_domain_using_staticmem zero if undefined
- extract common codes for assigning pages into a helper assign_domstatic_pages
- refine commit message
- remove stub function acquire_reserved_page
- Alloc/free of memory can happen concurrently. So access to rsv_page_list
needs to be protected with a spinlock
---
v4 changes:
- commit message refinement
- miss dropping __init in acquire_domstatic_pages
- add the page back to the reserved list in case of error
- remove redundant printk
- refine log message and make it warn level
- guard "is_domain_using_staticmem" under CONFIG_STATIC_MEMORY
- #define is_domain_using_staticmem zero if undefined
---
v3 changes:
- fix possible racy issue in free_staticmem_pages()
- introduce a stub free_staticmem_pages() for the !CONFIG_STATIC_MEMORY case
- move the change to free_heap_pages() to cover other potential call sites
- change fixed width type uint32_t to unsigned int
- change "flags" to a more descriptive name "cdf"
- change name from "is_domain_static()" to "is_domain_using_staticmem"
- have page_list_del() just once out of the if()
- remove resv_pages counter
- make arch_free_heap_page be an expression, not a compound statement.
- move #ifndef is_domain_using_staticmem to the common header file
- remove #ifdef CONFIG_STATIC_MEMORY-ary
- remove meaningless page_to_mfn(page) in error log
---
v2 changes:
- let "flags" live in the struct domain. So other arch can take
advantage of it in the future
- change name from "is_domain_on_static_allocation" to "is_domain_static()"
- put reserved pages on resv_page_list after having taken them off
the "normal" list
- introduce acquire_reserved_page to retrieve reserved pages from
resv_page_list
- forbid non-zero-order requests in populate_physmap
- let is_domain_static return ((void)(d), false) on x86
- fix coding style

Penny Zheng (9):
  xen/arm: rename PGC_reserved to PGC_static
  xen: do not free reserved memory into heap
  xen: update SUPPORT.md for static allocation
  xen: do not merge reserved pages in free_heap_pages()
  xen: add field "flags" to cover all internal CDF_XXX
  xen/arm: introduce CDF_staticmem
  xen/arm: unpopulate memory when domain is static
  xen: introduce prepare_staticmem_pages
  xen: retrieve reserved pages on populate_physmap

 SUPPORT.md                        |   7 ++
 xen/arch/arm/domain.c             |   2 -
 xen/arch/arm/domain_build.c       |   5 +-
 xen/arch/arm/include/asm/domain.h |   3 +-
 xen/arch/arm/include/asm/mm.h     |  20 +++-
 xen/common/domain.c               |   7 ++
 xen/common/memory.c               |  23 +++++
 xen/common/page_alloc.c           | 149 ++++++++++++++++++++----------
 xen/include/xen/domain.h          |   8 ++
 xen/include/xen/mm.h              |   7 +-
 xen/include/xen/sched.h           |   6 ++
 11 files changed, 178 insertions(+), 59 deletions(-)

-- 
2.25.1

[PATCH v6 1/9] xen/arm: rename PGC_reserved to PGC_static

[Penny Zheng]

PGC_reserved could be ambiguous, and we have to tell what the pages are
reserved for, so this commit intends to rename PGC_reserved to
PGC_static, which clearly indicates the page is reserved for static
memory.

Signed-off-by: Penny Zheng <penny.zheng@arm.com>
---
v6 changes:
- rename PGC_staticmem to PGC_static
---
v5 changes:
- new commit
---
 xen/arch/arm/include/asm/mm.h |  6 +++---
 xen/common/page_alloc.c       | 22 +++++++++++-----------
 2 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/xen/arch/arm/include/asm/mm.h b/xen/arch/arm/include/asm/mm.h
index 424aaf2823..fbff11c468 100644
--- a/xen/arch/arm/include/asm/mm.h
+++ b/xen/arch/arm/include/asm/mm.h
@@ -108,9 +108,9 @@ struct page_info
   /* Page is Xen heap? */
 #define _PGC_xen_heap     PG_shift(2)
 #define PGC_xen_heap      PG_mask(1, 2)
-  /* Page is reserved */
-#define _PGC_reserved     PG_shift(3)
-#define PGC_reserved      PG_mask(1, 3)
+  /* Page is static memory */
+#define _PGC_static    PG_shift(3)
+#define PGC_static     PG_mask(1, 3)
 /* ... */
 /* Page is broken? */
 #define _PGC_broken       PG_shift(7)
diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 319029140f..9e5c757847 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -151,8 +151,8 @@
 #define p2m_pod_offline_or_broken_replace(pg) BUG_ON(pg != NULL)
 #endif
 
-#ifndef PGC_reserved
-#define PGC_reserved 0
+#ifndef PGC_static
+#define PGC_static 0
 #endif
 
 /*
@@ -2286,7 +2286,7 @@ int assign_pages(
 
         for ( i = 0; i < nr; i++ )
         {
-            ASSERT(!(pg[i].count_info & ~(PGC_extra | PGC_reserved)));
+            ASSERT(!(pg[i].count_info & ~(PGC_extra | PGC_static)));
             if ( pg[i].count_info & PGC_extra )
                 extra_pages++;
         }
@@ -2346,7 +2346,7 @@ int assign_pages(
         page_set_owner(&pg[i], d);
         smp_wmb(); /* Domain pointer must be visible before updating refcnt. */
         pg[i].count_info =
-            (pg[i].count_info & (PGC_extra | PGC_reserved)) | PGC_allocated | 1;
+            (pg[i].count_info & (PGC_extra | PGC_static)) | PGC_allocated | 1;
 
         page_list_add_tail(&pg[i], page_to_list(d, &pg[i]));
     }
@@ -2652,8 +2652,8 @@ void __init free_staticmem_pages(struct page_info *pg, unsigned long nr_mfns,
             scrub_one_page(pg);
         }
 
-        /* In case initializing page of static memory, mark it PGC_reserved. */
-        pg[i].count_info |= PGC_reserved;
+        /* In case initializing page of static memory, mark it PGC_static. */
+        pg[i].count_info |= PGC_static;
     }
 }
 
@@ -2682,8 +2682,8 @@ static struct page_info * __init acquire_staticmem_pages(mfn_t smfn,
 
     for ( i = 0; i < nr_mfns; i++ )
     {
-        /* The page should be reserved and not yet allocated. */
-        if ( pg[i].count_info != (PGC_state_free | PGC_reserved) )
+        /* The page should be static and not yet allocated. */
+        if ( pg[i].count_info != (PGC_state_free | PGC_static) )
         {
             printk(XENLOG_ERR
                    "pg[%lu] Static MFN %"PRI_mfn" c=%#lx t=%#x\n",
@@ -2697,10 +2697,10 @@ static struct page_info * __init acquire_staticmem_pages(mfn_t smfn,
                                 &tlbflush_timestamp);
 
         /*
-         * Preserve flag PGC_reserved and change page state
+         * Preserve flag PGC_static and change page state
          * to PGC_state_inuse.
          */
-        pg[i].count_info = PGC_reserved | PGC_state_inuse;
+        pg[i].count_info = PGC_static | PGC_state_inuse;
         /* Initialise fields which have other uses for free pages. */
         pg[i].u.inuse.type_info = 0;
         page_set_owner(&pg[i], NULL);
@@ -2722,7 +2722,7 @@ static struct page_info * __init acquire_staticmem_pages(mfn_t smfn,
 
  out_err:
     while ( i-- )
-        pg[i].count_info = PGC_reserved | PGC_state_free;
+        pg[i].count_info = PGC_static | PGC_state_free;
 
     spin_unlock(&heap_lock);
 
-- 
2.25.1

[PATCH v6 2/9] xen: do not free reserved memory into heap

[Penny Zheng]

Pages used as guest RAM for static domain, shall be reserved to this
domain only.
So in case reserved pages being used for other purpose, users
shall not free them back to heap, even when last ref gets dropped.

free_staticmem_pages will be called by free_heap_pages in runtime
for static domain freeing memory resource, so let's drop the __init
flag.

Signed-off-by: Penny Zheng <penny.zheng@arm.com>
---
v6 changes:
- adapt to PGC_static
- remove #ifdef aroud function declaration
---
v5 changes:
- In order to avoid stub functions, we #define PGC_staticmem to non-zero only
when CONFIG_STATIC_MEMORY
- use "unlikely()" around pg->count_info & PGC_staticmem
- remove pointless "if", since mark_page_free() is going to set count_info
to PGC_state_free and by consequence clear PGC_staticmem
- move #define PGC_staticmem 0 to mm.h
---
v4 changes:
- no changes
---
v3 changes:
- fix possible racy issue in free_staticmem_pages()
- introduce a stub free_staticmem_pages() for the !CONFIG_STATIC_MEMORY case
- move the change to free_heap_pages() to cover other potential call sites
- fix the indentation
---
v2 changes:
- new commit
---
 xen/arch/arm/include/asm/mm.h |  4 +++-
 xen/common/page_alloc.c       | 12 +++++++++---
 xen/include/xen/mm.h          |  2 --
 3 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/xen/arch/arm/include/asm/mm.h b/xen/arch/arm/include/asm/mm.h
index fbff11c468..7442893e77 100644
--- a/xen/arch/arm/include/asm/mm.h
+++ b/xen/arch/arm/include/asm/mm.h
@@ -108,9 +108,11 @@ struct page_info
   /* Page is Xen heap? */
 #define _PGC_xen_heap     PG_shift(2)
 #define PGC_xen_heap      PG_mask(1, 2)
-  /* Page is static memory */
+#ifdef CONFIG_STATIC_MEMORY
+/* Page is static memory */
 #define _PGC_static    PG_shift(3)
 #define PGC_static     PG_mask(1, 3)
+#endif
 /* ... */
 /* Page is broken? */
 #define _PGC_broken       PG_shift(7)
diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 9e5c757847..6876869fa6 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -1443,6 +1443,13 @@ static void free_heap_pages(
 
     ASSERT(order <= MAX_ORDER);
 
+    if ( unlikely(pg->count_info & PGC_static) )
+    {
+        /* Pages of static memory shall not go back to the heap. */
+        free_staticmem_pages(pg, 1UL << order, need_scrub);
+        return;
+    }
+
     spin_lock(&heap_lock);
 
     for ( i = 0; i < (1 << order); i++ )
@@ -2636,8 +2643,8 @@ struct domain *get_pg_owner(domid_t domid)
 
 #ifdef CONFIG_STATIC_MEMORY
 /* Equivalent of free_heap_pages to free nr_mfns pages of static memory. */
-void __init free_staticmem_pages(struct page_info *pg, unsigned long nr_mfns,
-                                 bool need_scrub)
+void free_staticmem_pages(struct page_info *pg, unsigned long nr_mfns,
+                          bool need_scrub)
 {
     mfn_t mfn = page_to_mfn(pg);
     unsigned long i;
@@ -2652,7 +2659,6 @@ void __init free_staticmem_pages(struct page_info *pg, unsigned long nr_mfns,
             scrub_one_page(pg);
         }
 
-        /* In case initializing page of static memory, mark it PGC_static. */
         pg[i].count_info |= PGC_static;
     }
 }
diff --git a/xen/include/xen/mm.h b/xen/include/xen/mm.h
index 3be754da92..1c4ddb336b 100644
--- a/xen/include/xen/mm.h
+++ b/xen/include/xen/mm.h
@@ -85,13 +85,11 @@ bool scrub_free_pages(void);
 } while ( false )
 #define FREE_XENHEAP_PAGE(p) FREE_XENHEAP_PAGES(p, 0)
 
-#ifdef CONFIG_STATIC_MEMORY
 /* These functions are for static memory */
 void free_staticmem_pages(struct page_info *pg, unsigned long nr_mfns,
                           bool need_scrub);
 int acquire_domstatic_pages(struct domain *d, mfn_t smfn, unsigned int nr_mfns,
                             unsigned int memflags);
-#endif
 
 /* Map machine page range in Xen virtual address space. */
 int map_pages_to_xen(
-- 
2.25.1

[PATCH v6 3/9] xen: update SUPPORT.md for static allocation

[Penny Zheng]

SUPPORT.md doesn't seem to explicitly say whether static memory is
supported, so this commit updates SUPPORT.md to add feature static
allocation tech preview for now.

Signed-off-by: Penny Zheng <penny.zheng@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
---
v6 changes:
- use domain instead of sub-systems
---
v5 changes:
- new commit
---
 SUPPORT.md | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/SUPPORT.md b/SUPPORT.md
index ee2cd319e2..f50bc3a0fd 100644
--- a/SUPPORT.md
+++ b/SUPPORT.md
@@ -278,6 +278,13 @@ to boot with memory < maxmem.
 
     Status, x86 HVM: Supported
 
+### Static Allocation
+
+Static allocation refers to domains for which memory areas are
+pre-defined by configuration using physical address ranges.
+
+    Status, ARM: Tech Preview
+
 ### Memory Sharing
 
 Allow sharing of identical pages between guests
-- 
2.25.1

[PATCH v6 4/9] xen: do not merge reserved pages in free_heap_pages()

[Penny Zheng]

The code in free_heap_pages() will try to merge pages with the
successor/predecessor if pages are suitably aligned. So if the pages
reserved are right next to the pages given to the heap allocator,
free_heap_pages() will merge them, and give the reserved pages to heap
allocator accidently as a result.

So in order to avoid the above scenario, this commit updates free_heap_pages()
to check whether the predecessor and/or successor has PGC_reserved set,
when trying to merge the about-to-be-freed chunk with the predecessor
and/or successor.

Suggested-by: Julien Grall <jgrall@amazon.com>
Signed-off-by: Penny Zheng <penny.zheng@arm.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Julien Grall <jgrall@amazon.com>
---
v6 changes:
- adapt to PGC_static
---
v5 changes:
- change PGC_reserved to adapt to PGC_staticmem
---
v4 changes:
- no changes
---
v3 changes:
- no changes
---
v2 changes:
- new commit
---
 xen/common/page_alloc.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 6876869fa6..7fb28e2e07 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -1486,6 +1486,7 @@ static void free_heap_pages(
             /* Merge with predecessor block? */
             if ( !mfn_valid(page_to_mfn(predecessor)) ||
                  !page_state_is(predecessor, free) ||
+                 (predecessor->count_info & PGC_static) ||
                  (PFN_ORDER(predecessor) != order) ||
                  (phys_to_nid(page_to_maddr(predecessor)) != node) )
                 break;
@@ -1509,6 +1510,7 @@ static void free_heap_pages(
             /* Merge with successor block? */
             if ( !mfn_valid(page_to_mfn(successor)) ||
                  !page_state_is(successor, free) ||
+                 (successor->count_info & PGC_static) ||
                  (PFN_ORDER(successor) != order) ||
                  (phys_to_nid(page_to_maddr(successor)) != node) )
                 break;
-- 
2.25.1

[PATCH v6 5/9] xen: add field "flags" to cover all internal CDF_XXX

[Penny Zheng]

With more and more CDF_xxx internal flags in and to save the space, this
commit introduces a new field "flags" in struct domain to store CDF_*
internal flags directly.

Another new CDF_xxx will be introduced in the next patch.

Signed-off-by: Penny Zheng <penny.zheng@arm.com>
Acked-by: Julien Grall <jgrall@amazon.com>
---
v6 changes:
- no change
---
v5 changes:
- no change
---
v4 changes:
- no change
---
v3 changes:
- change fixed width type uint32_t to unsigned int
- change "flags" to a more descriptive name "cdf"
---
v2 changes:
- let "flags" live in the struct domain. So other arch can take
advantage of it in the future
- fix coding style
---
 xen/arch/arm/domain.c             | 2 --
 xen/arch/arm/include/asm/domain.h | 3 +--
 xen/common/domain.c               | 3 +++
 xen/include/xen/sched.h           | 3 +++
 4 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
index 8110c1df86..74189d9878 100644
--- a/xen/arch/arm/domain.c
+++ b/xen/arch/arm/domain.c
@@ -709,8 +709,6 @@ int arch_domain_create(struct domain *d,
     ioreq_domain_init(d);
 #endif
 
-    d->arch.directmap = flags & CDF_directmap;
-
     /* p2m_init relies on some value initialized by the IOMMU subsystem */
     if ( (rc = iommu_domain_init(d, config->iommu_opts)) != 0 )
         goto fail;
diff --git a/xen/arch/arm/include/asm/domain.h b/xen/arch/arm/include/asm/domain.h
index ed63c2b6f9..fe7a029ebf 100644
--- a/xen/arch/arm/include/asm/domain.h
+++ b/xen/arch/arm/include/asm/domain.h
@@ -29,7 +29,7 @@ enum domain_type {
 #define is_64bit_domain(d) (0)
 #endif
 
-#define is_domain_direct_mapped(d) (d)->arch.directmap
+#define is_domain_direct_mapped(d) ((d)->cdf & CDF_directmap)
 
 /*
  * Is the domain using the host memory layout?
@@ -103,7 +103,6 @@ struct arch_domain
     void *tee;
 #endif
 
-    bool directmap;
 }  __cacheline_aligned;
 
 struct arch_vcpu
diff --git a/xen/common/domain.c b/xen/common/domain.c
index 7570eae91a..a3ef991bd1 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -567,6 +567,9 @@ struct domain *domain_create(domid_t domid,
     /* Sort out our idea of is_system_domain(). */
     d->domain_id = domid;
 
+    /* Holding CDF_* internal flags. */
+    d->cdf = flags;
+
     /* Debug sanity. */
     ASSERT(is_system_domain(d) ? config == NULL : config != NULL);
 
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index 463d41ffb6..5191853c18 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -596,6 +596,9 @@ struct domain
         struct ioreq_server     *server[MAX_NR_IOREQ_SERVERS];
     } ioreq_server;
 #endif
+
+    /* Holding CDF_* constant. Internal flags for domain creation. */
+    unsigned int cdf;
 };
 
 static inline struct page_list_head *page_to_list(
-- 
2.25.1

[PATCH v6 6/9] xen/arm: introduce CDF_staticmem

[Penny Zheng]

In order to have an easy and quick way to find out whether this domain memory
is statically configured, this commit introduces a new flag CDF_staticmem and a
new helper is_domain_using_staticmem() to tell.

Signed-off-by: Penny Zheng <penny.zheng@arm.com>
---
v6 changes:
- move non-zero is_domain_using_staticmem() from ARM header to common
header
---
v5 changes:
- guard "is_domain_using_staticmem" under CONFIG_STATIC_MEMORY
- #define is_domain_using_staticmem zero if undefined
---
v4 changes:
- no changes
---
v3 changes:
- change name from "is_domain_static()" to "is_domain_using_staticmem"
---
v2 changes:
- change name from "is_domain_on_static_allocation" to "is_domain_static()"
---
 xen/arch/arm/domain_build.c | 5 ++++-
 xen/include/xen/domain.h    | 8 ++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index 7ddd16c26d..f6e2e44c1e 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -3287,9 +3287,12 @@ void __init create_domUs(void)
         if ( !dt_device_is_compatible(node, "xen,domain") )
             continue;
 
+        if ( dt_find_property(node, "xen,static-mem", NULL) )
+            flags |= CDF_staticmem;
+
         if ( dt_property_read_bool(node, "direct-map") )
         {
-            if ( !IS_ENABLED(CONFIG_STATIC_MEMORY) || !dt_find_property(node, "xen,static-mem", NULL) )
+            if ( !IS_ENABLED(CONFIG_STATIC_MEMORY) || !(flags & CDF_staticmem) )
                 panic("direct-map is not valid for domain %s without static allocation.\n",
                       dt_node_name(node));
 
diff --git a/xen/include/xen/domain.h b/xen/include/xen/domain.h
index 1c3c88a14d..c847452414 100644
--- a/xen/include/xen/domain.h
+++ b/xen/include/xen/domain.h
@@ -34,6 +34,14 @@ void arch_get_domain_info(const struct domain *d,
 #ifdef CONFIG_ARM
 /* Should domain memory be directly mapped? */
 #define CDF_directmap            (1U << 1)
+/* Is domain memory on static allocation? */
+#define CDF_staticmem            (1U << 2)
+#endif
+
+#ifdef CONFIG_STATIC_MEMORY
+#define is_domain_using_staticmem(d) ((d)->cdf & CDF_staticmem)
+#else
+#define is_domain_using_staticmem(d) ((void)(d), false)
 #endif
 
 /*
-- 
2.25.1

[PATCH v6 7/9] xen/arm: unpopulate memory when domain is static

[Penny Zheng]

Today when a domain unpopulates the memory on runtime, they will always
hand the memory back to the heap allocator. And it will be a problem if domain
is static.

Pages as guest RAM for static domain shall be reserved to only this domain
and not be used for any other purposes, so they shall never go back to heap
allocator.

This commit puts reserved pages on the new list resv_page_list only after
having taken them off the "normal" list, when the last ref dropped.

Signed-off-by: Penny Zheng <penny.zheng@arm.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
---
v6 changes:
- refine in-code comment
- move PGC_static !CONFIG_STATIC_MEMORY definition to common header
---
v5 changes:
- adapt this patch for PGC_staticmem
---
v4 changes:
- no changes
---
v3 changes:
- have page_list_del() just once out of the if()
- remove resv_pages counter
- make arch_free_heap_page be an expression, not a compound statement.
---
v2 changes:
- put reserved pages on resv_page_list after having taken them off
the "normal" list
---
 xen/arch/arm/include/asm/mm.h | 12 ++++++++++++
 xen/common/domain.c           |  4 ++++
 xen/common/page_alloc.c       |  4 ----
 xen/include/xen/mm.h          |  4 ++++
 xen/include/xen/sched.h       |  3 +++
 5 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/xen/arch/arm/include/asm/mm.h b/xen/arch/arm/include/asm/mm.h
index 7442893e77..2ce4d80796 100644
--- a/xen/arch/arm/include/asm/mm.h
+++ b/xen/arch/arm/include/asm/mm.h
@@ -360,6 +360,18 @@ void clear_and_clean_page(struct page_info *page);
 
 unsigned int arch_get_dma_bitsize(void);
 
+/*
+ * Put free pages on the resv page list after having taken them
+ * off the "normal" page list, when pages from static memory
+ */
+#ifdef CONFIG_STATIC_MEMORY
+#define arch_free_heap_page(d, pg) ({                   \
+    page_list_del(pg, page_to_list(d, pg));             \
+    if ( (pg)->count_info & PGC_static )              \
+        page_list_add_tail(pg, &(d)->resv_page_list);   \
+})
+#endif
+
 #endif /*  __ARCH_ARM_MM__ */
 /*
  * Local variables:
diff --git a/xen/common/domain.c b/xen/common/domain.c
index a3ef991bd1..a49574fa24 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -604,6 +604,10 @@ struct domain *domain_create(domid_t domid,
     INIT_PAGE_LIST_HEAD(&d->page_list);
     INIT_PAGE_LIST_HEAD(&d->extra_page_list);
     INIT_PAGE_LIST_HEAD(&d->xenpage_list);
+#ifdef CONFIG_STATIC_MEMORY
+    INIT_PAGE_LIST_HEAD(&d->resv_page_list);
+#endif
+
 
     spin_lock_init(&d->node_affinity_lock);
     d->node_affinity = NODE_MASK_ALL;
diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 7fb28e2e07..886b5d82a2 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -151,10 +151,6 @@
 #define p2m_pod_offline_or_broken_replace(pg) BUG_ON(pg != NULL)
 #endif
 
-#ifndef PGC_static
-#define PGC_static 0
-#endif
-
 /*
  * Comma-separated list of hexadecimal page numbers containing bad bytes.
  * e.g. 'badpage=0x3f45,0x8a321'.
diff --git a/xen/include/xen/mm.h b/xen/include/xen/mm.h
index 1c4ddb336b..e80b4bdcde 100644
--- a/xen/include/xen/mm.h
+++ b/xen/include/xen/mm.h
@@ -210,6 +210,10 @@ extern struct domain *dom_cow;
 
 #include <asm/mm.h>
 
+#ifndef PGC_static
+#define PGC_static 0
+#endif
+
 static inline bool is_special_page(const struct page_info *page)
 {
     return is_xen_heap_page(page) || (page->count_info & PGC_extra);
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index 5191853c18..bd2782b3c5 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -381,6 +381,9 @@ struct domain
     struct page_list_head page_list;  /* linked list */
     struct page_list_head extra_page_list; /* linked list (size extra_pages) */
     struct page_list_head xenpage_list; /* linked list (size xenheap_pages) */
+#ifdef CONFIG_STATIC_MEMORY
+    struct page_list_head resv_page_list; /* linked list */
+#endif
 
     /*
      * This field should only be directly accessed by domain_adjust_tot_pages()
-- 
2.25.1

[PATCH v6 8/9] xen: introduce prepare_staticmem_pages

[Penny Zheng]

Later, we want to use acquire_domstatic_pages() for populating memory
for static domain on runtime, however, there are a lot of pointless work
(checking mfn_valid(), scrubbing the free part, cleaning the cache...)
considering we know the page is valid and belong to the guest.

This commit splits acquire_staticmem_pages() in two parts, and
introduces prepare_staticmem_pages to bypass all "pointless work".

Signed-off-by: Penny Zheng <penny.zheng@arm.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
---
v6 changes:
- adapt to PGC_static
---
v5 changes:
- new commit
---
 xen/common/page_alloc.c | 61 ++++++++++++++++++++++++-----------------
 1 file changed, 36 insertions(+), 25 deletions(-)

diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 886b5d82a2..9004dd41c1 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -2661,26 +2661,13 @@ void free_staticmem_pages(struct page_info *pg, unsigned long nr_mfns,
     }
 }
 
-/*
- * Acquire nr_mfns contiguous reserved pages, starting at #smfn, of
- * static memory.
- * This function needs to be reworked if used outside of boot.
- */
-static struct page_info * __init acquire_staticmem_pages(mfn_t smfn,
-                                                         unsigned long nr_mfns,
-                                                         unsigned int memflags)
+static bool __init prepare_staticmem_pages(struct page_info *pg,
+                                           unsigned long nr_mfns,
+                                           unsigned int memflags)
 {
     bool need_tlbflush = false;
     uint32_t tlbflush_timestamp = 0;
     unsigned long i;
-    struct page_info *pg;
-
-    ASSERT(nr_mfns);
-    for ( i = 0; i < nr_mfns; i++ )
-        if ( !mfn_valid(mfn_add(smfn, i)) )
-            return NULL;
-
-    pg = mfn_to_page(smfn);
 
     spin_lock(&heap_lock);
 
@@ -2691,7 +2678,7 @@ static struct page_info * __init acquire_staticmem_pages(mfn_t smfn,
         {
             printk(XENLOG_ERR
                    "pg[%lu] Static MFN %"PRI_mfn" c=%#lx t=%#x\n",
-                   i, mfn_x(smfn) + i,
+                   i, mfn_x(page_to_mfn(pg)) + i,
                    pg[i].count_info, pg[i].tlbflush_timestamp);
             goto out_err;
         }
@@ -2715,6 +2702,38 @@ static struct page_info * __init acquire_staticmem_pages(mfn_t smfn,
     if ( need_tlbflush )
         filtered_flush_tlb_mask(tlbflush_timestamp);
 
+    return true;
+
+ out_err:
+    while ( i-- )
+        pg[i].count_info = PGC_static | PGC_state_free;
+
+    spin_unlock(&heap_lock);
+
+    return false;
+}
+
+/*
+ * Acquire nr_mfns contiguous reserved pages, starting at #smfn, of
+ * static memory.
+ * This function needs to be reworked if used outside of boot.
+ */
+static struct page_info * __init acquire_staticmem_pages(mfn_t smfn,
+                                                         unsigned long nr_mfns,
+                                                         unsigned int memflags)
+{
+    unsigned long i;
+    struct page_info *pg;
+
+    ASSERT(nr_mfns);
+    for ( i = 0; i < nr_mfns; i++ )
+        if ( !mfn_valid(mfn_add(smfn, i)) )
+            return NULL;
+
+    pg = mfn_to_page(smfn);
+    if ( !prepare_staticmem_pages(pg, nr_mfns, memflags) )
+        return NULL;
+
     /*
      * Ensure cache and RAM are consistent for platforms where the guest
      * can control its own visibility of/through the cache.
@@ -2723,14 +2742,6 @@ static struct page_info * __init acquire_staticmem_pages(mfn_t smfn,
         flush_page_to_ram(mfn_x(smfn) + i, !(memflags & MEMF_no_icache_flush));
 
     return pg;
-
- out_err:
-    while ( i-- )
-        pg[i].count_info = PGC_static | PGC_state_free;
-
-    spin_unlock(&heap_lock);
-
-    return NULL;
 }
 
 /*
-- 
2.25.1

[PATCH v6 9/9] xen: retrieve reserved pages on populate_physmap

[Penny Zheng]

When a static domain populates memory through populate_physmap at runtime,
it shall retrieve reserved pages from resv_page_list to make sure that
guest RAM is still restricted in statically configured memory regions.
This commit also introduces a new helper acquire_reserved_page to make it work.

Signed-off-by: Penny Zheng <penny.zheng@arm.com>
---
v6 changes:
- drop the lock before returning
---
v5 changes:
- extract common codes for assigning pages into a helper assign_domstatic_pages
- refine commit message
- remove stub function acquire_reserved_page
- Alloc/free of memory can happen concurrently. So access to rsv_page_list
needs to be protected with a spinlock
---
v4 changes：
- miss dropping __init in acquire_domstatic_pages
- add the page back to the reserved list in case of error
- remove redundant printk
- refine log message and make it warn level
---
v3 changes:
- move is_domain_using_staticmem to the common header file
- remove #ifdef CONFIG_STATIC_MEMORY-ary
- remove meaningless page_to_mfn(page) in error log
---
v2 changes:
- introduce acquire_reserved_page to retrieve reserved pages from
resv_page_list
- forbid non-zero-order requests in populate_physmap
- let is_domain_static return ((void)(d), false) on x86
---
 xen/common/memory.c     | 23 ++++++++++++++
 xen/common/page_alloc.c | 70 +++++++++++++++++++++++++++++++----------
 xen/include/xen/mm.h    |  1 +
 3 files changed, 77 insertions(+), 17 deletions(-)

diff --git a/xen/common/memory.c b/xen/common/memory.c
index f2d009843a..cb330ce877 100644
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -245,6 +245,29 @@ static void populate_physmap(struct memop_args *a)
 
                 mfn = _mfn(gpfn);
             }
+            else if ( is_domain_using_staticmem(d) )
+            {
+                /*
+                 * No easy way to guarantee the retrieved pages are contiguous,
+                 * so forbid non-zero-order requests here.
+                 */
+                if ( a->extent_order != 0 )
+                {
+                    gdprintk(XENLOG_WARNING,
+                             "Cannot allocate static order-%u pages for static %pd\n",
+                             a->extent_order, d);
+                    goto out;
+                }
+
+                mfn = acquire_reserved_page(d, a->memflags);
+                if ( mfn_eq(mfn, INVALID_MFN) )
+                {
+                    gdprintk(XENLOG_WARNING,
+                             "%pd: failed to retrieve a reserved page\n",
+                             d);
+                    goto out;
+                }
+            }
             else
             {
                 page = alloc_domheap_pages(d, a->extent_order, a->memflags);
diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 9004dd41c1..57d28304df 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -2661,9 +2661,8 @@ void free_staticmem_pages(struct page_info *pg, unsigned long nr_mfns,
     }
 }
 
-static bool __init prepare_staticmem_pages(struct page_info *pg,
-                                           unsigned long nr_mfns,
-                                           unsigned int memflags)
+static bool prepare_staticmem_pages(struct page_info *pg, unsigned long nr_mfns,
+                                    unsigned int memflags)
 {
     bool need_tlbflush = false;
     uint32_t tlbflush_timestamp = 0;
@@ -2744,21 +2743,9 @@ static struct page_info * __init acquire_staticmem_pages(mfn_t smfn,
     return pg;
 }
 
-/*
- * Acquire nr_mfns contiguous pages, starting at #smfn, of static memory,
- * then assign them to one specific domain #d.
- */
-int __init acquire_domstatic_pages(struct domain *d, mfn_t smfn,
-                                   unsigned int nr_mfns, unsigned int memflags)
+static int assign_domstatic_pages(struct domain *d, struct page_info *pg,
+                                  unsigned int nr_mfns, unsigned int memflags)
 {
-    struct page_info *pg;
-
-    ASSERT(!in_irq());
-
-    pg = acquire_staticmem_pages(smfn, nr_mfns, memflags);
-    if ( !pg )
-        return -ENOENT;
-
     if ( !d || (memflags & (MEMF_no_owner | MEMF_no_refcount)) )
     {
         /*
@@ -2777,6 +2764,55 @@ int __init acquire_domstatic_pages(struct domain *d, mfn_t smfn,
 
     return 0;
 }
+
+/*
+ * Acquire nr_mfns contiguous pages, starting at #smfn, of static memory,
+ * then assign them to one specific domain #d.
+ */
+int __init acquire_domstatic_pages(struct domain *d, mfn_t smfn,
+                                   unsigned int nr_mfns, unsigned int memflags)
+{
+    struct page_info *pg;
+
+    ASSERT(!in_irq());
+
+    pg = acquire_staticmem_pages(smfn, nr_mfns, memflags);
+    if ( !pg )
+        return -ENOENT;
+
+    if ( assign_domstatic_pages(d, pg, nr_mfns, memflags) )
+        return -EINVAL;
+
+    return 0;
+}
+
+/*
+ * Acquire a page from reserved page list(resv_page_list), when populating
+ * memory for static domain on runtime.
+ */
+mfn_t acquire_reserved_page(struct domain *d, unsigned int memflags)
+{
+    struct page_info *page;
+
+    spin_lock(&d->page_alloc_lock);
+    /* Acquire a page from reserved page list(resv_page_list). */
+    page = page_list_remove_head(&d->resv_page_list);
+    spin_unlock(&d->page_alloc_lock);
+    if ( unlikely(!page) )
+        return INVALID_MFN;
+
+    if ( !prepare_staticmem_pages(page, 1, memflags) )
+        goto fail;
+
+    if ( assign_domstatic_pages(d, page, 1, memflags) )
+        goto fail;
+
+    return page_to_mfn(page);
+
+ fail:
+    page_list_add_tail(page, &d->resv_page_list);
+    return INVALID_MFN;
+}
 #endif
 
 /*
diff --git a/xen/include/xen/mm.h b/xen/include/xen/mm.h
index e80b4bdcde..e100151e50 100644
--- a/xen/include/xen/mm.h
+++ b/xen/include/xen/mm.h
@@ -90,6 +90,7 @@ void free_staticmem_pages(struct page_info *pg, unsigned long nr_mfns,
                           bool need_scrub);
 int acquire_domstatic_pages(struct domain *d, mfn_t smfn, unsigned int nr_mfns,
                             unsigned int memflags);
+mfn_t acquire_reserved_page(struct domain *d, unsigned int memflags);
 
 /* Map machine page range in Xen virtual address space. */
 int map_pages_to_xen(
-- 
2.25.1

Re: [PATCH v6 1/9] xen/arm: rename PGC_reserved to PGC_static

[Jan Beulich]

On 07.06.2022 09:30, Penny Zheng wrote:
> PGC_reserved could be ambiguous, and we have to tell what the pages are
> reserved for, so this commit intends to rename PGC_reserved to
> PGC_static, which clearly indicates the page is reserved for static
> memory.
> 
> Signed-off-by: Penny Zheng <penny.zheng@arm.com>

Acked-by: Jan Beulich <jbeulich@suse.com>

Re: [PATCH v6 2/9] xen: do not free reserved memory into heap

[Jan Beulich]

On 07.06.2022 09:30, Penny Zheng wrote:
> Pages used as guest RAM for static domain, shall be reserved to this
> domain only.
> So in case reserved pages being used for other purpose, users
> shall not free them back to heap, even when last ref gets dropped.
> 
> free_staticmem_pages will be called by free_heap_pages in runtime
> for static domain freeing memory resource, so let's drop the __init
> flag.
> 
> Signed-off-by: Penny Zheng <penny.zheng@arm.com>

Acked-by: Jan Beulich <jbeulich@suse.com>

Re: [PATCH v6 6/9] xen/arm: introduce CDF_staticmem

[Jan Beulich]

On 07.06.2022 09:30, Penny Zheng wrote:
> --- a/xen/arch/arm/domain_build.c
> +++ b/xen/arch/arm/domain_build.c
> @@ -3287,9 +3287,12 @@ void __init create_domUs(void)
>          if ( !dt_device_is_compatible(node, "xen,domain") )
>              continue;
>  
> +        if ( dt_find_property(node, "xen,static-mem", NULL) )
> +            flags |= CDF_staticmem;
> +
>          if ( dt_property_read_bool(node, "direct-map") )
>          {
> -            if ( !IS_ENABLED(CONFIG_STATIC_MEMORY) || !dt_find_property(node, "xen,static-mem", NULL) )
> +            if ( !IS_ENABLED(CONFIG_STATIC_MEMORY) || !(flags & CDF_staticmem) )
>                  panic("direct-map is not valid for domain %s without static allocation.\n",
>                        dt_node_name(node));

I think there's either a change needed elsewhere (which you may have in a
later patch, but which would look to belong here) or you may want to deal
right here with CDF_staticmem being invalid without STATIC_MEMORY:

        if ( IS_ENABLED(CONFIG_STATIC_MEMORY) &&
             dt_find_property(node, "xen,static-mem", NULL) )
            flags |= CDF_staticmem;

        if ( dt_property_read_bool(node, "direct-map") )
        {
            if ( !(flags & CDF_staticmem) )
                panic("direct-map is not valid for domain %s without static allocation.\n",
                      dt_node_name(node));

Another option would seem to be

/* Is domain memory on static allocation? */
#ifdef CONFIG_STATIC_MEMORY
# define CDF_staticmem            (1U << 2)
#else
# define CDF_staticmem            0
#endif

in xen/domain.h (at which point no IS_ENABLED() would be needed
anymore afaict).

Jan

Re: [PATCH v6 9/9] xen: retrieve reserved pages on populate_physmap

[Jan Beulich]

On 07.06.2022 09:30, Penny Zheng wrote:
> +/*
> + * Acquire a page from reserved page list(resv_page_list), when populating
> + * memory for static domain on runtime.
> + */
> +mfn_t acquire_reserved_page(struct domain *d, unsigned int memflags)
> +{
> +    struct page_info *page;
> +
> +    spin_lock(&d->page_alloc_lock);
> +    /* Acquire a page from reserved page list(resv_page_list). */
> +    page = page_list_remove_head(&d->resv_page_list);
> +    spin_unlock(&d->page_alloc_lock);

With page removal done under lock, ...

> +    if ( unlikely(!page) )
> +        return INVALID_MFN;
> +
> +    if ( !prepare_staticmem_pages(page, 1, memflags) )
> +        goto fail;
> +
> +    if ( assign_domstatic_pages(d, page, 1, memflags) )
> +        goto fail;
> +
> +    return page_to_mfn(page);
> +
> + fail:
> +    page_list_add_tail(page, &d->resv_page_list);
> +    return INVALID_MFN;

... doesn't re-adding the page to the list also need to be done
with the lock held?

Jan

Re: [PATCH v6 1/9] xen/arm: rename PGC_reserved to PGC_static

[Julien Grall]

Hi,

On 07/06/2022 08:30, Penny Zheng wrote:
> PGC_reserved could be ambiguous, and we have to tell what the pages are
> reserved for, so this commit intends to rename PGC_reserved to
> PGC_static, which clearly indicates the page is reserved for static
> memory.
> 
> Signed-off-by: Penny Zheng <penny.zheng@arm.com>

Acked-by: Julien Grall <jgrall@amazon.com>

Cheers,

> ---
> v6 changes:
> - rename PGC_staticmem to PGC_static
> ---
> v5 changes:
> - new commit
> ---
>   xen/arch/arm/include/asm/mm.h |  6 +++---
>   xen/common/page_alloc.c       | 22 +++++++++++-----------
>   2 files changed, 14 insertions(+), 14 deletions(-)
> 
> diff --git a/xen/arch/arm/include/asm/mm.h b/xen/arch/arm/include/asm/mm.h
> index 424aaf2823..fbff11c468 100644
> --- a/xen/arch/arm/include/asm/mm.h
> +++ b/xen/arch/arm/include/asm/mm.h
> @@ -108,9 +108,9 @@ struct page_info
>     /* Page is Xen heap? */
>   #define _PGC_xen_heap     PG_shift(2)
>   #define PGC_xen_heap      PG_mask(1, 2)
> -  /* Page is reserved */
> -#define _PGC_reserved     PG_shift(3)
> -#define PGC_reserved      PG_mask(1, 3)
> +  /* Page is static memory */
> +#define _PGC_static    PG_shift(3)
> +#define PGC_static     PG_mask(1, 3)
>   /* ... */
>   /* Page is broken? */
>   #define _PGC_broken       PG_shift(7)
> diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
> index 319029140f..9e5c757847 100644
> --- a/xen/common/page_alloc.c
> +++ b/xen/common/page_alloc.c
> @@ -151,8 +151,8 @@
>   #define p2m_pod_offline_or_broken_replace(pg) BUG_ON(pg != NULL)
>   #endif
>   
> -#ifndef PGC_reserved
> -#define PGC_reserved 0
> +#ifndef PGC_static
> +#define PGC_static 0
>   #endif
>   
>   /*
> @@ -2286,7 +2286,7 @@ int assign_pages(
>   
>           for ( i = 0; i < nr; i++ )
>           {
> -            ASSERT(!(pg[i].count_info & ~(PGC_extra | PGC_reserved)));
> +            ASSERT(!(pg[i].count_info & ~(PGC_extra | PGC_static)));
>               if ( pg[i].count_info & PGC_extra )
>                   extra_pages++;
>           }
> @@ -2346,7 +2346,7 @@ int assign_pages(
>           page_set_owner(&pg[i], d);
>           smp_wmb(); /* Domain pointer must be visible before updating refcnt. */
>           pg[i].count_info =
> -            (pg[i].count_info & (PGC_extra | PGC_reserved)) | PGC_allocated | 1;
> +            (pg[i].count_info & (PGC_extra | PGC_static)) | PGC_allocated | 1;
>   
>           page_list_add_tail(&pg[i], page_to_list(d, &pg[i]));
>       }
> @@ -2652,8 +2652,8 @@ void __init free_staticmem_pages(struct page_info *pg, unsigned long nr_mfns,
>               scrub_one_page(pg);
>           }
>   
> -        /* In case initializing page of static memory, mark it PGC_reserved. */
> -        pg[i].count_info |= PGC_reserved;
> +        /* In case initializing page of static memory, mark it PGC_static. */
> +        pg[i].count_info |= PGC_static;
>       }
>   }
>   
> @@ -2682,8 +2682,8 @@ static struct page_info * __init acquire_staticmem_pages(mfn_t smfn,
>   
>       for ( i = 0; i < nr_mfns; i++ )
>       {
> -        /* The page should be reserved and not yet allocated. */
> -        if ( pg[i].count_info != (PGC_state_free | PGC_reserved) )
> +        /* The page should be static and not yet allocated. */
> +        if ( pg[i].count_info != (PGC_state_free | PGC_static) )
>           {
>               printk(XENLOG_ERR
>                      "pg[%lu] Static MFN %"PRI_mfn" c=%#lx t=%#x\n",
> @@ -2697,10 +2697,10 @@ static struct page_info * __init acquire_staticmem_pages(mfn_t smfn,
>                                   &tlbflush_timestamp);
>   
>           /*
> -         * Preserve flag PGC_reserved and change page state
> +         * Preserve flag PGC_static and change page state
>            * to PGC_state_inuse.
>            */
> -        pg[i].count_info = PGC_reserved | PGC_state_inuse;
> +        pg[i].count_info = PGC_static | PGC_state_inuse;
>           /* Initialise fields which have other uses for free pages. */
>           pg[i].u.inuse.type_info = 0;
>           page_set_owner(&pg[i], NULL);
> @@ -2722,7 +2722,7 @@ static struct page_info * __init acquire_staticmem_pages(mfn_t smfn,
>   
>    out_err:
>       while ( i-- )
> -        pg[i].count_info = PGC_reserved | PGC_state_free;
> +        pg[i].count_info = PGC_static | PGC_state_free;
>   
>       spin_unlock(&heap_lock);
>   

-- 
Julien Grall

Re: [PATCH v6 2/9] xen: do not free reserved memory into heap

[Julien Grall]

Hi Penny,

On 07/06/2022 08:30, Penny Zheng wrote:
> Pages used as guest RAM for static domain, shall be reserved to this
> domain only.
> So in case reserved pages being used for other purpose, users
> shall not free them back to heap, even when last ref gets dropped.
> 
> free_staticmem_pages will be called by free_heap_pages in runtime
> for static domain freeing memory resource, so let's drop the __init
> flag.
> 
> Signed-off-by: Penny Zheng <penny.zheng@arm.com>
> ---
> v6 changes:
> - adapt to PGC_static
> - remove #ifdef aroud function declaration
> ---
> v5 changes:
> - In order to avoid stub functions, we #define PGC_staticmem to non-zero only
> when CONFIG_STATIC_MEMORY
> - use "unlikely()" around pg->count_info & PGC_staticmem
> - remove pointless "if", since mark_page_free() is going to set count_info
> to PGC_state_free and by consequence clear PGC_staticmem
> - move #define PGC_staticmem 0 to mm.h
> ---
> v4 changes:
> - no changes
> ---
> v3 changes:
> - fix possible racy issue in free_staticmem_pages()
> - introduce a stub free_staticmem_pages() for the !CONFIG_STATIC_MEMORY case
> - move the change to free_heap_pages() to cover other potential call sites
> - fix the indentation
> ---
> v2 changes:
> - new commit
> ---
>   xen/arch/arm/include/asm/mm.h |  4 +++-
>   xen/common/page_alloc.c       | 12 +++++++++---
>   xen/include/xen/mm.h          |  2 --
>   3 files changed, 12 insertions(+), 6 deletions(-)
> 
> diff --git a/xen/arch/arm/include/asm/mm.h b/xen/arch/arm/include/asm/mm.h
> index fbff11c468..7442893e77 100644
> --- a/xen/arch/arm/include/asm/mm.h
> +++ b/xen/arch/arm/include/asm/mm.h
> @@ -108,9 +108,11 @@ struct page_info
>     /* Page is Xen heap? */
>   #define _PGC_xen_heap     PG_shift(2)
>   #define PGC_xen_heap      PG_mask(1, 2)
> -  /* Page is static memory */

NITpicking: You added this comment in patch #1 and now removing the 
space. Any reason to drop the space?

> +#ifdef CONFIG_STATIC_MEMORY

I think this change ought to be explained in the commit message. AFAIU, 
this is necessary to allow the compiler to remove code and avoid linking 
issues. Is that correct?

> +/* Page is static memory */
>   #define _PGC_static    PG_shift(3)
>   #define PGC_static     PG_mask(1, 3)
> +#endif
>   /* ... */
>   /* Page is broken? */
>   #define _PGC_broken       PG_shift(7)
> diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
> index 9e5c757847..6876869fa6 100644
> --- a/xen/common/page_alloc.c
> +++ b/xen/common/page_alloc.c
> @@ -1443,6 +1443,13 @@ static void free_heap_pages(
>   
>       ASSERT(order <= MAX_ORDER);
>   
> +    if ( unlikely(pg->count_info & PGC_static) )
> +    {
> +        /* Pages of static memory shall not go back to the heap. */
> +        free_staticmem_pages(pg, 1UL << order, need_scrub);
I can't remember whether I asked this before (I couldn't find a thread).

free_staticmem_pages() doesn't seem to be protected by any lock. So how 
do you prevent the concurrent access to the page info with the acquire part?

Cheers,

-- 
Julien Grall

Re: [PATCH v6 7/9] xen/arm: unpopulate memory when domain is static

[Julien Grall]

Hi Penny,

On 07/06/2022 08:30, Penny Zheng wrote:
> Today when a domain unpopulates the memory on runtime, they will always
> hand the memory back to the heap allocator. And it will be a problem if domain
> is static.
> 
> Pages as guest RAM for static domain shall be reserved to only this domain
> and not be used for any other purposes, so they shall never go back to heap
> allocator.
> 
> This commit puts reserved pages on the new list resv_page_list only after
> having taken them off the "normal" list, when the last ref dropped.
> 
> Signed-off-by: Penny Zheng <penny.zheng@arm.com>
> Acked-by: Jan Beulich <jbeulich@suse.com>
> ---
> v6 changes:
> - refine in-code comment
> - move PGC_static !CONFIG_STATIC_MEMORY definition to common header

I don't understand why this change is necessary for this patch. AFAICT, 
all the users of PGC_static will be protected by #ifdef 
CONFIG_STATIC_MEMORY and therefore PGC_static should always be defined.

Cheers,

-- 
Julien Grall

RE: [PATCH v6 7/9] xen/arm: unpopulate memory when domain is static

[Penny Zheng]

Hi Julien

> -----Original Message-----
> From: Julien Grall <julien@xen.org>
> Sent: Tuesday, June 7, 2022 5:20 PM
> To: Penny Zheng <Penny.Zheng@arm.com>; xen-devel@lists.xenproject.org
> Cc: Wei Chen <Wei.Chen@arm.com>; Stefano Stabellini
> <sstabellini@kernel.org>; Bertrand Marquis <Bertrand.Marquis@arm.com>;
> Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>; Andrew Cooper
> <andrew.cooper3@citrix.com>; George Dunlap <george.dunlap@citrix.com>;
> Jan Beulich <jbeulich@suse.com>; Wei Liu <wl@xen.org>
> Subject: Re: [PATCH v6 7/9] xen/arm: unpopulate memory when domain is
> static
> 
> Hi Penny,
> 
> On 07/06/2022 08:30, Penny Zheng wrote:
> > Today when a domain unpopulates the memory on runtime, they will
> > always hand the memory back to the heap allocator. And it will be a
> > problem if domain is static.
> >
> > Pages as guest RAM for static domain shall be reserved to only this
> > domain and not be used for any other purposes, so they shall never go
> > back to heap allocator.
> >
> > This commit puts reserved pages on the new list resv_page_list only
> > after having taken them off the "normal" list, when the last ref dropped.
> >
> > Signed-off-by: Penny Zheng <penny.zheng@arm.com>
> > Acked-by: Jan Beulich <jbeulich@suse.com>
> > ---
> > v6 changes:
> > - refine in-code comment
> > - move PGC_static !CONFIG_STATIC_MEMORY definition to common header
> 
> I don't understand why this change is necessary for this patch. AFAICT, all the
> users of PGC_static will be protected by #ifdef CONFIG_STATIC_MEMORY and
> therefore PGC_static should always be defined.
> 

True, I notice that arch_free_heap_page has already been guarded with
#ifdef CONFIG_STATIC_MEMORY. I'll revert the change.

> Cheers,
> 
> --
> Julien Grall

RE: [PATCH v6 2/9] xen: do not free reserved memory into heap

[Penny Zheng]

> -----Original Message-----
> From: Julien Grall <julien@xen.org>
> Sent: Tuesday, June 7, 2022 5:13 PM
> To: Penny Zheng <Penny.Zheng@arm.com>; xen-devel@lists.xenproject.org
> Cc: Wei Chen <Wei.Chen@arm.com>; Stefano Stabellini
> <sstabellini@kernel.org>; Bertrand Marquis <Bertrand.Marquis@arm.com>;
> Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>; Andrew Cooper
> <andrew.cooper3@citrix.com>; George Dunlap <george.dunlap@citrix.com>;
> Jan Beulich <jbeulich@suse.com>; Wei Liu <wl@xen.org>
> Subject: Re: [PATCH v6 2/9] xen: do not free reserved memory into heap
> 
> Hi Penny,
> 

Hi Julien

> On 07/06/2022 08:30, Penny Zheng wrote:
> > Pages used as guest RAM for static domain, shall be reserved to this
> > domain only.
> > So in case reserved pages being used for other purpose, users shall
> > not free them back to heap, even when last ref gets dropped.
> >
> > free_staticmem_pages will be called by free_heap_pages in runtime for
> > static domain freeing memory resource, so let's drop the __init flag.
> >
> > Signed-off-by: Penny Zheng <penny.zheng@arm.com>
> > ---
> > v6 changes:
> > - adapt to PGC_static
> > - remove #ifdef aroud function declaration
> > ---
> > v5 changes:
> > - In order to avoid stub functions, we #define PGC_staticmem to
> > non-zero only when CONFIG_STATIC_MEMORY
> > - use "unlikely()" around pg->count_info & PGC_staticmem
> > - remove pointless "if", since mark_page_free() is going to set
> > count_info to PGC_state_free and by consequence clear PGC_staticmem
> > - move #define PGC_staticmem 0 to mm.h
> > ---
> > v4 changes:
> > - no changes
> > ---
> > v3 changes:
> > - fix possible racy issue in free_staticmem_pages()
> > - introduce a stub free_staticmem_pages() for the
> > !CONFIG_STATIC_MEMORY case
> > - move the change to free_heap_pages() to cover other potential call
> > sites
> > - fix the indentation
> > ---
> > v2 changes:
> > - new commit
> > ---
> >   xen/arch/arm/include/asm/mm.h |  4 +++-
> >   xen/common/page_alloc.c       | 12 +++++++++---
> >   xen/include/xen/mm.h          |  2 --
> >   3 files changed, 12 insertions(+), 6 deletions(-)
> >
> > diff --git a/xen/arch/arm/include/asm/mm.h
> > b/xen/arch/arm/include/asm/mm.h index fbff11c468..7442893e77 100644
> > --- a/xen/arch/arm/include/asm/mm.h
> > +++ b/xen/arch/arm/include/asm/mm.h
> > @@ -108,9 +108,11 @@ struct page_info
> >     /* Page is Xen heap? */
> >   #define _PGC_xen_heap     PG_shift(2)
> >   #define PGC_xen_heap      PG_mask(1, 2)
> > -  /* Page is static memory */
> 
> NITpicking: You added this comment in patch #1 and now removing the space.
> Any reason to drop the space?
> 
> > +#ifdef CONFIG_STATIC_MEMORY
> 
> I think this change ought to be explained in the commit message. AFAIU, this is
> necessary to allow the compiler to remove code and avoid linking issues. Is
> that correct?
> 
> > +/* Page is static memory */
> >   #define _PGC_static    PG_shift(3)
> >   #define PGC_static     PG_mask(1, 3)
> > +#endif
> >   /* ... */
> >   /* Page is broken? */
> >   #define _PGC_broken       PG_shift(7)
> > diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c index
> > 9e5c757847..6876869fa6 100644
> > --- a/xen/common/page_alloc.c
> > +++ b/xen/common/page_alloc.c
> > @@ -1443,6 +1443,13 @@ static void free_heap_pages(
> >
> >       ASSERT(order <= MAX_ORDER);
> >
> > +    if ( unlikely(pg->count_info & PGC_static) )
> > +    {
> > +        /* Pages of static memory shall not go back to the heap. */
> > +        free_staticmem_pages(pg, 1UL << order, need_scrub);
> I can't remember whether I asked this before (I couldn't find a thread).
> 
> free_staticmem_pages() doesn't seem to be protected by any lock. So how do
> you prevent the concurrent access to the page info with the acquire part?

True, last time you suggested that rsv_page_list needs to be protected with a
spinlock (mostly like d->page_alloc_lock). I haven't thought it thoroughly, sorry
about that.
So for freeing part, I shall get the lock at arch_free_heap_page(), where we insert
the page to the rsv_page_list, and release the lock at the end of the free_staticmem_page.
And for acquiring part, I've already put the lock around 
page = page_list_remove_head(&d->resv_page_list);

> Cheers,
> 
> --
> Julien Grall

RE: [PATCH v6 9/9] xen: retrieve reserved pages on populate_physmap

[Penny Zheng]

Hi Jan

> -----Original Message-----
> From: Jan Beulich <jbeulich@suse.com>
> Sent: Tuesday, June 7, 2022 3:58 PM
> To: Penny Zheng <Penny.Zheng@arm.com>
> Cc: Wei Chen <Wei.Chen@arm.com>; Andrew Cooper
> <andrew.cooper3@citrix.com>; George Dunlap <george.dunlap@citrix.com>;
> Julien Grall <julien@xen.org>; Stefano Stabellini <sstabellini@kernel.org>; Wei
> Liu <wl@xen.org>; xen-devel@lists.xenproject.org
> Subject: Re: [PATCH v6 9/9] xen: retrieve reserved pages on populate_physmap
> 
> On 07.06.2022 09:30, Penny Zheng wrote:
> > +/*
> > + * Acquire a page from reserved page list(resv_page_list), when
> > +populating
> > + * memory for static domain on runtime.
> > + */
> > +mfn_t acquire_reserved_page(struct domain *d, unsigned int memflags)
> > +{
> > +    struct page_info *page;
> > +
> > +    spin_lock(&d->page_alloc_lock);
> > +    /* Acquire a page from reserved page list(resv_page_list). */
> > +    page = page_list_remove_head(&d->resv_page_list);
> > +    spin_unlock(&d->page_alloc_lock);
> 
> With page removal done under lock, ...
> 
> > +    if ( unlikely(!page) )
> > +        return INVALID_MFN;
> > +
> > +    if ( !prepare_staticmem_pages(page, 1, memflags) )
> > +        goto fail;
> > +
> > +    if ( assign_domstatic_pages(d, page, 1, memflags) )
> > +        goto fail;
> > +
> > +    return page_to_mfn(page);
> > +
> > + fail:
> > +    page_list_add_tail(page, &d->resv_page_list);
> > +    return INVALID_MFN;
> 
> ... doesn't re-adding the page to the list also need to be done with the lock
> held?

True, Sorry about that.
Like I said in another thread with Julien, I'll add the missing half part
"
For freeing part, I shall get the lock at arch_free_heap_page(),
where we insert the page to the rsv_page_list, and release the lock at the end of
the free_staticmem_page
"

> 
> Jan

Re: [PATCH v6 2/9] xen: do not free reserved memory into heap

[Julien Grall]

Hi,

On 09/06/2022 06:54, Penny Zheng wrote:
> 
> 
>> -----Original Message-----
>> From: Julien Grall <julien@xen.org>
>> Sent: Tuesday, June 7, 2022 5:13 PM
>> To: Penny Zheng <Penny.Zheng@arm.com>; xen-devel@lists.xenproject.org
>> Cc: Wei Chen <Wei.Chen@arm.com>; Stefano Stabellini
>> <sstabellini@kernel.org>; Bertrand Marquis <Bertrand.Marquis@arm.com>;
>> Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>; Andrew Cooper
>> <andrew.cooper3@citrix.com>; George Dunlap <george.dunlap@citrix.com>;
>> Jan Beulich <jbeulich@suse.com>; Wei Liu <wl@xen.org>
>> Subject: Re: [PATCH v6 2/9] xen: do not free reserved memory into heap
>>
>> Hi Penny,
>>
> 
> Hi Julien
> 
>> On 07/06/2022 08:30, Penny Zheng wrote:
>>> Pages used as guest RAM for static domain, shall be reserved to this
>>> domain only.
>>> So in case reserved pages being used for other purpose, users shall
>>> not free them back to heap, even when last ref gets dropped.
>>>
>>> free_staticmem_pages will be called by free_heap_pages in runtime for
>>> static domain freeing memory resource, so let's drop the __init flag.
>>>
>>> Signed-off-by: Penny Zheng <penny.zheng@arm.com>
>>> ---
>>> v6 changes:
>>> - adapt to PGC_static
>>> - remove #ifdef aroud function declaration
>>> ---
>>> v5 changes:
>>> - In order to avoid stub functions, we #define PGC_staticmem to
>>> non-zero only when CONFIG_STATIC_MEMORY
>>> - use "unlikely()" around pg->count_info & PGC_staticmem
>>> - remove pointless "if", since mark_page_free() is going to set
>>> count_info to PGC_state_free and by consequence clear PGC_staticmem
>>> - move #define PGC_staticmem 0 to mm.h
>>> ---
>>> v4 changes:
>>> - no changes
>>> ---
>>> v3 changes:
>>> - fix possible racy issue in free_staticmem_pages()
>>> - introduce a stub free_staticmem_pages() for the
>>> !CONFIG_STATIC_MEMORY case
>>> - move the change to free_heap_pages() to cover other potential call
>>> sites
>>> - fix the indentation
>>> ---
>>> v2 changes:
>>> - new commit
>>> ---
>>>    xen/arch/arm/include/asm/mm.h |  4 +++-
>>>    xen/common/page_alloc.c       | 12 +++++++++---
>>>    xen/include/xen/mm.h          |  2 --
>>>    3 files changed, 12 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/xen/arch/arm/include/asm/mm.h
>>> b/xen/arch/arm/include/asm/mm.h index fbff11c468..7442893e77 100644
>>> --- a/xen/arch/arm/include/asm/mm.h
>>> +++ b/xen/arch/arm/include/asm/mm.h
>>> @@ -108,9 +108,11 @@ struct page_info
>>>      /* Page is Xen heap? */
>>>    #define _PGC_xen_heap     PG_shift(2)
>>>    #define PGC_xen_heap      PG_mask(1, 2)
>>> -  /* Page is static memory */
>>
>> NITpicking: You added this comment in patch #1 and now removing the space.
>> Any reason to drop the space?
>>
>>> +#ifdef CONFIG_STATIC_MEMORY
>>
>> I think this change ought to be explained in the commit message. AFAIU, this is
>> necessary to allow the compiler to remove code and avoid linking issues. Is
>> that correct?
>>
>>> +/* Page is static memory */
>>>    #define _PGC_static    PG_shift(3)
>>>    #define PGC_static     PG_mask(1, 3)
>>> +#endif
>>>    /* ... */
>>>    /* Page is broken? */
>>>    #define _PGC_broken       PG_shift(7)
>>> diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c index
>>> 9e5c757847..6876869fa6 100644
>>> --- a/xen/common/page_alloc.c
>>> +++ b/xen/common/page_alloc.c
>>> @@ -1443,6 +1443,13 @@ static void free_heap_pages(
>>>
>>>        ASSERT(order <= MAX_ORDER);
>>>
>>> +    if ( unlikely(pg->count_info & PGC_static) )
>>> +    {
>>> +        /* Pages of static memory shall not go back to the heap. */
>>> +        free_staticmem_pages(pg, 1UL << order, need_scrub);
>> I can't remember whether I asked this before (I couldn't find a thread).
>>
>> free_staticmem_pages() doesn't seem to be protected by any lock. So how do
>> you prevent the concurrent access to the page info with the acquire part?
> 
> True, last time you suggested that rsv_page_list needs to be protected with a
> spinlock (mostly like d->page_alloc_lock). I haven't thought it thoroughly, sorry
> about that.
> So for freeing part, I shall get the lock at arch_free_heap_page(), where we insert
> the page to the rsv_page_list, and release the lock at the end of the free_staticmem_page.

In general, a lock is better to be lock/unlock in the same function 
because it is easier to verify. However, I am not sure that extending 
the locking from d->page_alloc_lock up after free_heap_pages() is right.

The first reason being that they are other callers of free_heap_pages(). 
So now all the callers of the helpers would need to know whether they 
need to help d->page_alloc_lock.

Secondly, free_staticmem_pages() is meant to be the reverse of 
prepare_staticmem_pages(). We should prevent both of them to be called 
concurrently. It sounds strange to use the d->page_alloc_lock to protect 
it (a page is technically not belonging to a domain at this point).

To me it looks like we want to add the pages on the rsv_page_list 
*after* the pages have been freed. So we know that all the pages on that 
list have been marked as freed (i.e. free_staticmem_pages() completed).

In addition to that, we would need the code in free_staticmem_pages() to 
be protected by the heap_lock (at least so it is match 
prepare_staticmem_pages()).

Any thoughts?

Cheers,

-- 
Julien Grall

RE: [PATCH v6 2/9] xen: do not free reserved memory into heap

[Penny Zheng]

Hi Julien

> -----Original Message-----
> From: Julien Grall <julien@xen.org>
> Sent: Thursday, June 9, 2022 5:22 PM
> To: Penny Zheng <Penny.Zheng@arm.com>; xen-devel@lists.xenproject.org
> Cc: Wei Chen <Wei.Chen@arm.com>; Stefano Stabellini
> <sstabellini@kernel.org>; Bertrand Marquis <Bertrand.Marquis@arm.com>;
> Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>; Andrew Cooper
> <andrew.cooper3@citrix.com>; George Dunlap <george.dunlap@citrix.com>;
> Jan Beulich <jbeulich@suse.com>; Wei Liu <wl@xen.org>
> Subject: Re: [PATCH v6 2/9] xen: do not free reserved memory into heap
> 
> Hi,
> 
> On 09/06/2022 06:54, Penny Zheng wrote:
> >
> >
> >> -----Original Message-----
> >> From: Julien Grall <julien@xen.org>
> >> Sent: Tuesday, June 7, 2022 5:13 PM
> >> To: Penny Zheng <Penny.Zheng@arm.com>; xen-devel@lists.xenproject.org
> >> Cc: Wei Chen <Wei.Chen@arm.com>; Stefano Stabellini
> >> <sstabellini@kernel.org>; Bertrand Marquis
> >> <Bertrand.Marquis@arm.com>; Volodymyr Babchuk
> >> <Volodymyr_Babchuk@epam.com>; Andrew Cooper
> >> <andrew.cooper3@citrix.com>; George Dunlap
> >> <george.dunlap@citrix.com>; Jan Beulich <jbeulich@suse.com>; Wei Liu
> >> <wl@xen.org>
> >> Subject: Re: [PATCH v6 2/9] xen: do not free reserved memory into
> >> heap
> >>
> >> Hi Penny,
> >>
> >
> > Hi Julien
> >
> >> On 07/06/2022 08:30, Penny Zheng wrote:
> >>> Pages used as guest RAM for static domain, shall be reserved to this
> >>> domain only.
> >>> So in case reserved pages being used for other purpose, users shall
> >>> not free them back to heap, even when last ref gets dropped.
> >>>
> >>> free_staticmem_pages will be called by free_heap_pages in runtime
> >>> for static domain freeing memory resource, so let's drop the __init flag.
> >>>
> >>> Signed-off-by: Penny Zheng <penny.zheng@arm.com>
> >>> ---
> >>> v6 changes:
> >>> - adapt to PGC_static
> >>> - remove #ifdef aroud function declaration
> >>> ---
> >>> v5 changes:
> >>> - In order to avoid stub functions, we #define PGC_staticmem to
> >>> non-zero only when CONFIG_STATIC_MEMORY
> >>> - use "unlikely()" around pg->count_info & PGC_staticmem
> >>> - remove pointless "if", since mark_page_free() is going to set
> >>> count_info to PGC_state_free and by consequence clear PGC_staticmem
> >>> - move #define PGC_staticmem 0 to mm.h
> >>> ---
> >>> v4 changes:
> >>> - no changes
> >>> ---
> >>> v3 changes:
> >>> - fix possible racy issue in free_staticmem_pages()
> >>> - introduce a stub free_staticmem_pages() for the
> >>> !CONFIG_STATIC_MEMORY case
> >>> - move the change to free_heap_pages() to cover other potential call
> >>> sites
> >>> - fix the indentation
> >>> ---
> >>> v2 changes:
> >>> - new commit
> >>> ---
> >>>    xen/arch/arm/include/asm/mm.h |  4 +++-
> >>>    xen/common/page_alloc.c       | 12 +++++++++---
> >>>    xen/include/xen/mm.h          |  2 --
> >>>    3 files changed, 12 insertions(+), 6 deletions(-)
> >>>
> >>> diff --git a/xen/arch/arm/include/asm/mm.h
> >>> b/xen/arch/arm/include/asm/mm.h index fbff11c468..7442893e77 100644
> >>> --- a/xen/arch/arm/include/asm/mm.h
> >>> +++ b/xen/arch/arm/include/asm/mm.h
> >>> @@ -108,9 +108,11 @@ struct page_info
> >>>      /* Page is Xen heap? */
> >>>    #define _PGC_xen_heap     PG_shift(2)
> >>>    #define PGC_xen_heap      PG_mask(1, 2)
> >>> -  /* Page is static memory */
> >>
> >> NITpicking: You added this comment in patch #1 and now removing the
> space.
> >> Any reason to drop the space?
> >>
> >>> +#ifdef CONFIG_STATIC_MEMORY
> >>
> >> I think this change ought to be explained in the commit message.
> >> AFAIU, this is necessary to allow the compiler to remove code and
> >> avoid linking issues. Is that correct?
> >>
> >>> +/* Page is static memory */
> >>>    #define _PGC_static    PG_shift(3)
> >>>    #define PGC_static     PG_mask(1, 3)
> >>> +#endif
> >>>    /* ... */
> >>>    /* Page is broken? */
> >>>    #define _PGC_broken       PG_shift(7)
> >>> diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c index
> >>> 9e5c757847..6876869fa6 100644
> >>> --- a/xen/common/page_alloc.c
> >>> +++ b/xen/common/page_alloc.c
> >>> @@ -1443,6 +1443,13 @@ static void free_heap_pages(
> >>>
> >>>        ASSERT(order <= MAX_ORDER);
> >>>
> >>> +    if ( unlikely(pg->count_info & PGC_static) )
> >>> +    {
> >>> +        /* Pages of static memory shall not go back to the heap. */
> >>> +        free_staticmem_pages(pg, 1UL << order, need_scrub);
> >> I can't remember whether I asked this before (I couldn't find a thread).
> >>
> >> free_staticmem_pages() doesn't seem to be protected by any lock. So
> >> how do you prevent the concurrent access to the page info with the acquire
> part?
> >
> > True, last time you suggested that rsv_page_list needs to be protected
> > with a spinlock (mostly like d->page_alloc_lock). I haven't thought it
> > thoroughly, sorry about that.
> > So for freeing part, I shall get the lock at arch_free_heap_page(),
> > where we insert the page to the rsv_page_list, and release the lock at the
> end of the free_staticmem_page.
> 
> In general, a lock is better to be lock/unlock in the same function because it is
> easier to verify. However, I am not sure that extending the locking from d-
> >page_alloc_lock up after free_heap_pages() is right.
> 
> The first reason being that they are other callers of free_heap_pages().
> So now all the callers of the helpers would need to know whether they need to
> help d->page_alloc_lock.
> 
> Secondly, free_staticmem_pages() is meant to be the reverse of
> prepare_staticmem_pages(). We should prevent both of them to be called
> concurrently. It sounds strange to use the d->page_alloc_lock to protect it (a
> page is technically not belonging to a domain at this point).
> 
> To me it looks like we want to add the pages on the rsv_page_list
> *after* the pages have been freed. So we know that all the pages on that list
> have been marked as freed (i.e. free_staticmem_pages() completed).
> 

Yes! That fixes everything!
If we add the pages on the rsv_page_list *after* the pages have been freed, we
could make sure that page acquired from rsv_page_list has been totally freed.
Hmmm, so in such case, do we still need to add lock here? 
We already could make sure that page acquired from rsv_page_list must be totally
freed, without the lock.
Or in facts, we use the lock to let prepare_staticmem_pages() not fail if free_staticmem_pages
happen concurrently?
Trying to understand the intents of the lock here more clearly, hope it's not a dumb question~

`> In addition to that, we would need the code in free_staticmem_pages() to be
> protected by the heap_lock (at least so it is match
> prepare_staticmem_pages()).
> 
> Any thoughts?
> 
> Cheers,
> 
> --
> Julien Grall