[PATCH v2 01/26] xen: arm: update p2m_set_allocation() prototype

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

p2m_set_allocation() signals preemption redundantly: via a bool *preempted
out-argument (set to true) and via -ERESTART return code, both at the same
time. This led to the caller-side ASSERT(preempted == (rc == -ERESTART))
added solely to document their agreement.

Drop the out-argument entirely. The return code alone is sufficient to
distinguish preemption (-ERESTART) from success (0) or other failures.
Replace the pointer with a plain bool can_preempt that controls whether
the preemption check is performed at all, making the previous
NULL-to-suppress-preemption calling convention explicit and type-safe.

Since p2m_set_allocation() is called by the common dom0less build code,
move its declaration from the ARM-specific asm/p2m.h to xen/p2m-common.h.

Reported-by: Jan Beulich <jbeulich@xxxxxxxx>
Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
Changes in v2:
 - new patch
---
 xen/arch/arm/include/asm/p2m.h          |  1 -
 xen/arch/arm/mmu/p2m.c                  | 22 ++++++++--------------
 xen/arch/riscv/include/asm/paging.h     |  2 +-
 xen/arch/riscv/p2m.c                    |  7 ++++---
 xen/arch/riscv/paging.c                 |  7 ++-----
 xen/common/device-tree/dom0less-build.c |  2 +-
 xen/include/xen/p2m-common.h            |  2 ++
 7 files changed, 18 insertions(+), 25 deletions(-)

diff --git a/xen/arch/arm/include/asm/p2m.h b/xen/arch/arm/include/asm/p2m.h
index 7957dbd96e57..62b37a05f79e 100644
--- a/xen/arch/arm/include/asm/p2m.h
+++ b/xen/arch/arm/include/asm/p2m.h
@@ -232,7 +232,6 @@ void p2m_restore_state(struct vcpu *n);
 /* Print debugging/statistial info about a domain's p2m */
 void p2m_dump_info(struct domain *d);
 
-int p2m_set_allocation(struct domain *d, unsigned long pages, bool *preempted);
 int p2m_teardown_allocation(struct domain *d);
 
 static inline void p2m_write_lock(struct p2m_domain *p2m)
diff --git a/xen/arch/arm/mmu/p2m.c b/xen/arch/arm/mmu/p2m.c
index 51abf3504fcf..e5c6be7c0890 100644
--- a/xen/arch/arm/mmu/p2m.c
+++ b/xen/arch/arm/mmu/p2m.c
@@ -67,10 +67,11 @@ int arch_get_paging_mempool_size(struct domain *d, uint64_t 
*size)
 
 /*
  * Set the pool of pages to the required number of pages.
- * Returns 0 for success, non-zero for failure.
+ * Returns 0 for success, -ERESTART if preempted, or a negative error code on
+ * failure.
  * Call with d->arch.paging.lock held.
  */
-int p2m_set_allocation(struct domain *d, unsigned long pages, bool *preempted)
+int p2m_set_allocation(struct domain *d, unsigned long pages, bool can_preempt)
 {
     struct page_info *pg;
 
@@ -112,11 +113,8 @@ int p2m_set_allocation(struct domain *d, unsigned long 
pages, bool *preempted)
             break;
 
         /* Check to see if we need to yield and try again */
-        if ( preempted && general_preempt_check() )
-        {
-            *preempted = true;
+        if ( can_preempt && general_preempt_check() )
             return -ERESTART;
-        }
     }
 
     return 0;
@@ -125,7 +123,6 @@ int p2m_set_allocation(struct domain *d, unsigned long 
pages, bool *preempted)
 int arch_set_paging_mempool_size(struct domain *d, uint64_t size)
 {
     unsigned long pages = size >> PAGE_SHIFT;
-    bool preempted = false;
     int rc;
 
     if ( (size & ~PAGE_MASK) ||          /* Non page-sized request? */
@@ -133,27 +130,24 @@ int arch_set_paging_mempool_size(struct domain *d, 
uint64_t size)
         return -EINVAL;
 
     spin_lock(&d->arch.paging.lock);
-    rc = p2m_set_allocation(d, pages, &preempted);
+    rc = p2m_set_allocation(d, pages, true);
     spin_unlock(&d->arch.paging.lock);
 
-    ASSERT(preempted == (rc == -ERESTART));
-
     return rc;
 }
 
 int p2m_teardown_allocation(struct domain *d)
 {
     int ret = 0;
-    bool preempted = false;
 
     spin_lock(&d->arch.paging.lock);
     if ( d->arch.paging.p2m_total_pages != 0 )
     {
-        ret = p2m_set_allocation(d, 0, &preempted);
-        if ( preempted )
+        ret = p2m_set_allocation(d, 0, true);
+        if ( ret == -ERESTART )
         {
             spin_unlock(&d->arch.paging.lock);
-            return -ERESTART;
+            return ret;
         }
         ASSERT(d->arch.paging.p2m_total_pages == 0);
     }
diff --git a/xen/arch/riscv/include/asm/paging.h 
b/xen/arch/riscv/include/asm/paging.h
index e487c89a4ccd..103384723dc5 100644
--- a/xen/arch/riscv/include/asm/paging.h
+++ b/xen/arch/riscv/include/asm/paging.h
@@ -9,7 +9,7 @@ struct page_info;
 int paging_domain_init(struct domain *d);
 
 int paging_freelist_adjust(struct domain *d, unsigned long pages,
-                           bool *preempted);
+                           bool can_preempt);
 
 int paging_ret_to_domheap(struct domain *d, unsigned int nr_pages);
 int paging_refill_from_domheap(struct domain *d, unsigned int nr_pages);
diff --git a/xen/arch/riscv/p2m.c b/xen/arch/riscv/p2m.c
index 703b9f4d2540..41d6d3d5e699 100644
--- a/xen/arch/riscv/p2m.c
+++ b/xen/arch/riscv/p2m.c
@@ -430,15 +430,16 @@ int p2m_init(struct domain *d, const struct 
xen_domctl_createdomain *config)
 
 /*
  * Set the pool of pages to the required number of pages.
- * Returns 0 for success, non-zero for failure.
+ * Returns 0 for success, -ERESTART if preempted, or a negative error code on
+ * failure.
  * Call with d->arch.paging.lock held.
  */
-int p2m_set_allocation(struct domain *d, unsigned long pages, bool *preempted)
+int p2m_set_allocation(struct domain *d, unsigned long pages, bool can_preempt)
 {
     struct p2m_domain *p2m = p2m_get_hostp2m(d);
     int rc;
 
-    if ( (rc = paging_freelist_adjust(d, pages, preempted)) )
+    if ( (rc = paging_freelist_adjust(d, pages, can_preempt)) )
         return rc;
 
     /*
diff --git a/xen/arch/riscv/paging.c b/xen/arch/riscv/paging.c
index 76a203edbb0c..35f572689a7c 100644
--- a/xen/arch/riscv/paging.c
+++ b/xen/arch/riscv/paging.c
@@ -47,7 +47,7 @@ static int _paging_add_to_freelist(struct domain *d)
 }
 
 int paging_freelist_adjust(struct domain *d, unsigned long pages,
-                           bool *preempted)
+                           bool can_preempt)
 {
     ASSERT(spin_is_locked(&d->arch.paging.lock));
 
@@ -66,11 +66,8 @@ int paging_freelist_adjust(struct domain *d, unsigned long 
pages,
             return rc;
 
         /* Check to see if we need to yield and try again */
-        if ( preempted && general_preempt_check() )
-        {
-            *preempted = true;
+        if ( can_preempt && general_preempt_check() )
             return -ERESTART;
-        }
     }
 
     return 0;
diff --git a/xen/common/device-tree/dom0less-build.c 
b/xen/common/device-tree/dom0less-build.c
index 6d6882a34b5a..1058699ab25b 100644
--- a/xen/common/device-tree/dom0less-build.c
+++ b/xen/common/device-tree/dom0less-build.c
@@ -747,7 +747,7 @@ static int __init domain_p2m_set_allocation(struct domain 
*d, uint64_t mem,
                 domain_p2m_pages(mem, d->max_vcpus);
 
     spin_lock(&d->arch.paging.lock);
-    rc = p2m_set_allocation(d, p2m_pages, NULL);
+    rc = p2m_set_allocation(d, p2m_pages, false);
     spin_unlock(&d->arch.paging.lock);
 
     return rc;
diff --git a/xen/include/xen/p2m-common.h b/xen/include/xen/p2m-common.h
index f0bd9a6b9896..1b44ec8ce36c 100644
--- a/xen/include/xen/p2m-common.h
+++ b/xen/include/xen/p2m-common.h
@@ -43,5 +43,7 @@ int __must_check check_get_page_from_gfn(struct domain *d, 
gfn_t gfn,
                                          bool readonly, p2m_type_t *p2mt_p,
                                          struct page_info **page_p);
 
+int p2m_set_allocation(struct domain *d, unsigned long pages,
+                       bool can_preempt);
 
 #endif /* _XEN_P2M_COMMON_H */
-- 
2.54.0