[v2,4/7] xen/riscv: add {set,clear}_fixmap() functions for managing fixmap entries

Commit Message

Oleksii Kurochko Dec. 11, 2024, 5:27 p.m. UTC

Introduce set_fixmap() and clear_fixmap() functions to manage mappings
in the fixmap region. The set_fixmap() function maps a 4k page ( as only L0
is expected to be updated; look at setup_fixmap_mappings() ) at a specified
fixmap entry using map_pages_to_xen(), while clear_fixmap() removes the
mapping from a fixmap entry by calling destroy_xen_mappings().

Both functions ensure that the operations succeed by asserting that their
respective calls (map_pages_to_xen() and destroy_xen_mappings()) return 0.
`BUG()` is added to trigger a failure if any issues occur during
the mapping or unmapping process.

Signed-off-by: Oleksii Kurochko <[e-mail]>
Acked-by: Jan Beulich <[e-mail]>
---
Changes in V2:
 - Update the commit message.
 - drop local variables from {set, clear}_fixmap(); use if (... != 0) + BUG().
---
 xen/arch/riscv/include/asm/fixmap.h |  5 +++++
 xen/arch/riscv/pt.c                 | 17 +++++++++++++++++
 2 files changed, 22 insertions(+)

Comments

Jan Beulich Dec. 12, 2024, 11:48 a.m. UTC | #1

On 11.12.2024 18:27, Oleksii Kurochko wrote:
> @@ -433,3 +434,19 @@ int __init populate_pt_range(unsigned long virt, unsigned long nr_mfns)
>  {
>      return pt_update(virt, INVALID_MFN, nr_mfns, PTE_POPULATE);
>  }
> +
> +/* Map a 4k page in a fixmap entry */
> +void set_fixmap(unsigned int map, mfn_t mfn, unsigned int flags)
> +{
> +    if ( map_pages_to_xen(FIXMAP_ADDR(map), mfn, 1, flags | PTE_SMALL) != 0 )
> +        BUG();
> +}
> +
> +/* Remove a mapping from a fixmap entry */
> +void clear_fixmap(unsigned int map)
> +{
> +    if ( destroy_xen_mappings(
> +            FIXMAP_ADDR(map),
> +            FIXMAP_ADDR(map) + PAGE_SIZE) != 0 )

There are multiple options of how to indent such wrapped lines in function
invocations, but this isn't one of them.

    if ( destroy_xen_mappings(
             FIXMAP_ADDR(map),
             FIXMAP_ADDR(map) + PAGE_SIZE) != 0 )

(arguments offset by 4 from the function name, which may not be a multiple
of 4 from the start of the line) or

    if ( destroy_xen_mappings(FIXMAP_ADDR(map),
                              FIXMAP_ADDR(map) + PAGE_SIZE) != 0 )

Jan

Patch

diff --git a/xen/arch/riscv/include/asm/fixmap.h b/xen/arch/riscv/include/asm/fixmap.h
index 818c8ce07b..e399a15f53 100644
--- a/xen/arch/riscv/include/asm/fixmap.h
+++ b/xen/arch/riscv/include/asm/fixmap.h
@@ -32,6 +32,11 @@ 
  */
 extern pte_t xen_fixmap[];
 
+/* Map a page in a fixmap entry */
+void set_fixmap(unsigned int map, mfn_t mfn, unsigned int flags);
+/* Remove a mapping from a fixmap entry */
+void clear_fixmap(unsigned int map);
+
 #define fix_to_virt(slot) ((void *)FIXMAP_ADDR(slot))
 
 static inline unsigned int virt_to_fix(vaddr_t vaddr)
diff --git a/xen/arch/riscv/pt.c b/xen/arch/riscv/pt.c
index 86bd9ea613..3407fda937 100644
--- a/xen/arch/riscv/pt.c
+++ b/xen/arch/riscv/pt.c
@@ -8,6 +8,7 @@ 
 #include <xen/pmap.h>
 #include <xen/spinlock.h>
 
+#include <asm/fixmap.h>
 #include <asm/flushtlb.h>
 #include <asm/page.h>
 
@@ -433,3 +434,19 @@  int __init populate_pt_range(unsigned long virt, unsigned long nr_mfns)
 {
     return pt_update(virt, INVALID_MFN, nr_mfns, PTE_POPULATE);
 }
+
+/* Map a 4k page in a fixmap entry */
+void set_fixmap(unsigned int map, mfn_t mfn, unsigned int flags)
+{
+    if ( map_pages_to_xen(FIXMAP_ADDR(map), mfn, 1, flags | PTE_SMALL) != 0 )
+        BUG();
+}
+
+/* Remove a mapping from a fixmap entry */
+void clear_fixmap(unsigned int map)
+{
+    if ( destroy_xen_mappings(
+            FIXMAP_ADDR(map),
+            FIXMAP_ADDR(map) + PAGE_SIZE) != 0 )
+        BUG();
+}