[for-4.19,v2] xen/vmap: Document the vmap header

Commit Message

Alejandro Vallejo July 3, 2024, 11:19 a.m. UTC

In it's current form it's rather cryptic for uninitiated, so this patch
documents everything in there to make it more palatable.

No functional change.

Signed-off-by: Alejandro Vallejo <[e-mail]>
---
v2:
  * Removed Doxygen-style markers on comments.
  * Added some missing documentations for the return types of __vmap().
  * s/range of ranges/set of ranges/ in __vmap()
  * Removed rationale from vmap_contig()
  * Fixed "arrray" typo.
  * Moved misplaced comment to vfree()
---
 xen/include/xen/vmap.h | 101 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 101 insertions(+)

Comments

Jan Beulich July 3, 2024, 11:58 a.m. UTC | #1

On 03.07.2024 13:19, Alejandro Vallejo wrote:
> +/*
> + * Unmaps a range of virtually contiguous memory from one of the vmap regions
> + *
> + * The system remembers internally how wide the mapping is and unmaps it all.

Seeing this is still taken verbatim ...

> + * It also can determine the vmap region type from the `va`.
> + *
> + * @param va Virtual base address of the range to unmap
> + */
>  void vunmap(const void *va);
>  
> +/*
> + * Allocate `size` octets of possibly non-contiguous physical memory and map
> + * them contiguously in the VMAP_DEFAULT vmap region
> + *
> + * @param size Pointer to the base of an array of mfns
> + * @return Pointer to the mapped area on success; NULL otherwise.
> + */
>  void *vmalloc(size_t size);
> +
> +/* Same as vmalloc(), but for the VMAP_XEN vmap region. */
>  void *vmalloc_xen(size_t size);
>  
> +/* Same as vmalloc(), but set the contents to zero before returning */
>  void *vzalloc(size_t size);
> +
> +/*
> + * Unmap and free memory from vmalloc(), vmalloc_xen() or vzalloc()
> + *
> + * The system remembers internally how wide the mapping is and unmaps it all.
> + *
> + * @param va Virtual base address of the range to free and unmap
> + */
>  void vfree(void *va);

... here (just moved to the proper place now), I further wonder: Why just
"mapping" and "unmap". The function is also (one might even say primarily)
about freeing. IOW perhaps "how wide the allocation is and unmaps/frees it
all"?

Happy to adjust while committing, at which point:
Acked-by: Jan Beulich <[e-mail]>

Jan

Alejandro Vallejo July 3, 2024, 12:53 p.m. UTC | #2

On Wed Jul 3, 2024 at 12:58 PM BST, Jan Beulich wrote:
> On 03.07.2024 13:19, Alejandro Vallejo wrote:
> > +/*
> > + * Unmaps a range of virtually contiguous memory from one of the vmap regions
> > + *
> > + * The system remembers internally how wide the mapping is and unmaps it all.
>
> Seeing this is still taken verbatim ...
>
> > + * It also can determine the vmap region type from the `va`.
> > + *
> > + * @param va Virtual base address of the range to unmap
> > + */
> >  void vunmap(const void *va);
> >  
> > +/*
> > + * Allocate `size` octets of possibly non-contiguous physical memory and map
> > + * them contiguously in the VMAP_DEFAULT vmap region
> > + *
> > + * @param size Pointer to the base of an array of mfns
> > + * @return Pointer to the mapped area on success; NULL otherwise.
> > + */
> >  void *vmalloc(size_t size);
> > +
> > +/* Same as vmalloc(), but for the VMAP_XEN vmap region. */
> >  void *vmalloc_xen(size_t size);
> >  
> > +/* Same as vmalloc(), but set the contents to zero before returning */
> >  void *vzalloc(size_t size);
> > +
> > +/*
> > + * Unmap and free memory from vmalloc(), vmalloc_xen() or vzalloc()
> > + *
> > + * The system remembers internally how wide the mapping is and unmaps it all.
> > + *
> > + * @param va Virtual base address of the range to free and unmap
> > + */
> >  void vfree(void *va);
>
> ... here (just moved to the proper place now), I further wonder: Why just
> "mapping" and "unmap". The function is also (one might even say primarily)
> about freeing. IOW perhaps "how wide the allocation is and unmaps/frees it
> all"?
>
> Happy to adjust while committing, at which point:
> Acked-by: Jan Beulich <[e-mail]>
>
> Jan

Sounds good to me.

Cheers,
Alejandro

Oleksii Kurochko July 3, 2024, 1:51 p.m. UTC | #3

On Wed, 2024-07-03 at 13:58 +0200, Jan Beulich wrote:
> On 03.07.2024 13:19, Alejandro Vallejo wrote:
> > +/*
> > + * Unmaps a range of virtually contiguous memory from one of the
> > vmap regions
> > + *
> > + * The system remembers internally how wide the mapping is and
> > unmaps it all.
> 
> Seeing this is still taken verbatim ...
> 
> > + * It also can determine the vmap region type from the `va`.
> > + *
> > + * @param va Virtual base address of the range to unmap
> > + */
> >  void vunmap(const void *va);
> >  
> > +/*
> > + * Allocate `size` octets of possibly non-contiguous physical
> > memory and map
> > + * them contiguously in the VMAP_DEFAULT vmap region
> > + *
> > + * @param size Pointer to the base of an array of mfns
> > + * @return Pointer to the mapped area on success; NULL otherwise.
> > + */
> >  void *vmalloc(size_t size);
> > +
> > +/* Same as vmalloc(), but for the VMAP_XEN vmap region. */
> >  void *vmalloc_xen(size_t size);
> >  
> > +/* Same as vmalloc(), but set the contents to zero before
> > returning */
> >  void *vzalloc(size_t size);
> > +
> > +/*
> > + * Unmap and free memory from vmalloc(), vmalloc_xen() or
> > vzalloc()
> > + *
> > + * The system remembers internally how wide the mapping is and
> > unmaps it all.
> > + *
> > + * @param va Virtual base address of the range to free and unmap
> > + */
> >  void vfree(void *va);
> 
> ... here (just moved to the proper place now), I further wonder: Why
> just
> "mapping" and "unmap". The function is also (one might even say
> primarily)
> about freeing. IOW perhaps "how wide the allocation is and
> unmaps/frees it
> all"?
> 
> Happy to adjust while committing, at which point:
> Acked-by: Jan Beulich <[e-mail]>
Release-Acked-by: Oleksii Kurochko <[e-mail]>

~ Oleskii

Patch

diff --git a/xen/include/xen/vmap.h b/xen/include/xen/vmap.h
index 0c16baa85f31..1864e1ccfe82 100644
--- a/xen/include/xen/vmap.h
+++ b/xen/include/xen/vmap.h
@@ -1,34 +1,132 @@ 
+/*
+ * Interface to map physical memory onto contiguous virtual memory areas.
+ *
+ * Two ranges of linear address space are reserved for this purpose: A general
+ * purpose area (VMAP_DEFAULT) and a livepatch-specific area (VMAP_XEN). The
+ * latter is used when loading livepatches and the former for everything else.
+ */
 #if !defined(__XEN_VMAP_H__) && defined(VMAP_VIRT_START)
 #define __XEN_VMAP_H__
 
 #include <xen/mm-frame.h>
 #include <xen/page-size.h>
 
+/* Identifiers for the linear ranges tracked by vmap */
 enum vmap_region {
+    /*
+     * Region used for general purpose RW mappings. Mapping/allocating memory
+     * here can induce extra allocations for the supporting page tables.
+     */
     VMAP_DEFAULT,
+    /*
+     * Region used for loading livepatches. Can't use VMAP_DEFAULT because it
+     * must live close to the running Xen image. The caller also ensures all
+     * page tables are already in place with adequate PTE flags.
+     */
     VMAP_XEN,
+    /* Sentinel value for bounds checking */
     VMAP_REGION_NR,
 };
 
+/*
+ * Runtime initialiser for each vmap region type
+ *
+ * Must only be called once per vmap region type.
+ *
+ * @param type  Designation of the region to initialise.
+ * @param start Start address of the `type` region.
+ * @param end   End address (not inclusive) of the `type` region
+ */
 void vm_init_type(enum vmap_region type, void *start, void *end);
 
+/*
+ * Maps a set of physical ranges onto a single virtual range
+ *
+ * `mfn` is an array of `nr` physical ranges, each of which is `granularity`
+ * pages wide. `type` defines which vmap region to use for the mapping and
+ * `flags` is the PTE flags the page table leaves are meant to have.
+ *
+ * Typically used via the vmap() and vmap_contig() helpers.
+ *
+ * @param mfn          Array of mfns
+ * @param granularity  Number of contiguous pages each mfn represents
+ * @param nr           Number of mfns in the `mfn` array
+ * @param align        Alignment of the virtual area to map
+ * @param flags        PTE flags for the leaves of the PT tree.
+ * @param type         Which region to create the mappings on
+ * @return Pointer to the mapped area on success; NULL otherwise.
+ */
 void *__vmap(const mfn_t *mfn, unsigned int granularity, unsigned int nr,
              unsigned int align, unsigned int flags, enum vmap_region type);
+
+/*
+ * Map an array of pages contiguously into the VMAP_DEFAULT vmap region
+ *
+ * @param[in] mfn Pointer to the base of an array of mfns
+ * @param[in] nr  Number of mfns in the array
+ * @return Pointer to the mapped area on success; NULL otherwise.
+ */
 void *vmap(const mfn_t *mfn, unsigned int nr);
+
+/*
+ * Maps physically contiguous pages onto the VMAP_DEFAULT vmap region
+ *
+ * @param mfn Base mfn of the physical region
+ * @param nr  Number of mfns in the physical region
+ * @return Pointer to the mapped area on success; NULL otherwise.
+ */
 void *vmap_contig(mfn_t mfn, unsigned int nr);
+
+/*
+ * Unmaps a range of virtually contiguous memory from one of the vmap regions
+ *
+ * The system remembers internally how wide the mapping is and unmaps it all.
+ * It also can determine the vmap region type from the `va`.
+ *
+ * @param va Virtual base address of the range to unmap
+ */
 void vunmap(const void *va);
 
+/*
+ * Allocate `size` octets of possibly non-contiguous physical memory and map
+ * them contiguously in the VMAP_DEFAULT vmap region
+ *
+ * @param size Pointer to the base of an array of mfns
+ * @return Pointer to the mapped area on success; NULL otherwise.
+ */
 void *vmalloc(size_t size);
+
+/* Same as vmalloc(), but for the VMAP_XEN vmap region. */
 void *vmalloc_xen(size_t size);
 
+/* Same as vmalloc(), but set the contents to zero before returning */
 void *vzalloc(size_t size);
+
+/*
+ * Unmap and free memory from vmalloc(), vmalloc_xen() or vzalloc()
+ *
+ * The system remembers internally how wide the mapping is and unmaps it all.
+ *
+ * @param va Virtual base address of the range to free and unmap
+ */
 void vfree(void *va);
 
+/*
+ * Analogous to vmap_contig(), but for IO memory
+ *
+ * Unlike vmap_contig(), it ensures architecturally correct cacheability
+ * settings are set for the mapped IO memory.
+ *
+ * @param pa  Physical base address of the MMIO region.
+ * @param len Length of the MMIO region in octets.
+ * @return Pointer to the mapped area on success; NULL otherwise.
+ */
 void __iomem *ioremap(paddr_t pa, size_t len);
 
 /* Return the number of pages in the mapping starting at address 'va' */
 unsigned int vmap_size(const void *va);
 
+/* Analogous to vunmap(), but for IO memory mapped via ioremap() */
 static inline void iounmap(void __iomem *va)
 {
     unsigned long addr = (unsigned long)(void __force *)va;
@@ -36,7 +134,10 @@  static inline void iounmap(void __iomem *va)
     vunmap((void *)(addr & PAGE_MASK));
 }
 
+/* Pointer to 1 octet past the end of the VMAP_DEFAULT virtual area */
 void *arch_vmap_virt_end(void);
+
+/* Initialises the VMAP_DEFAULT virtual range */
 static inline void vm_init(void)
 {
     vm_init_type(VMAP_DEFAULT, (void *)VMAP_VIRT_START, arch_vmap_virt_end());