x86/gnttab: do not implement GNTTABOP_cache_flush

The current underlying implementation of GNTTABOP_cache_flush on x86 won't
work as expected.  The provided {clean,invalidate}_dcache_va_range()
helpers only do a local pCPU cache flush, so the cache of previous pCPUs
where the vCPU might have run are not flushed.

However instead of attempting to fix this, make the GNTTABOP_cache_flush
operation only available to ARM.  There are no known users on x86, the
implementation is broken, and other architectures don't have grant-table
support yet.

With that operation not implemented on x86, the related
{clean,invalidate}_dcache_va_range() helpers can also be removed.

Fixes: f62dc81c2d ("x86: introduce more cache maintenance operations")
Fixes: 18e8d22fe7 ("introduce GNTTABOP_cache_flush")
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-By: Oleksii Kurochko<oleksii.kurochko@gmail.com>
Acked-by: Julien Grall <jgrall@amazon.com>

CHANGELOG.md

@@ -28,6 +28,9 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
     - Ability to enable stack protector
 
 ### Removed
+ - On x86:
+   - GNTTABOP_cache_flush: it's unused on x86 and the implementation is
+     broken.
 
 ## [4.20.0](https://xenbits.xenproject.org/gitweb/?p=xen.git;a=shortlog;h=RELEASE-4.20.0) - 2025-03-05
 

xen/arch/arm/Kconfig

@@ -17,6 +17,7 @@ config ARM
 	select HAS_ALTERNATIVE if HAS_VMAP
 	select HAS_DEVICE_TREE
 	select HAS_DOM0LESS
+	select HAS_GRANT_CACHE_FLUSH if GRANT_TABLE
 	select HAS_STACK_PROTECTOR
 	select HAS_UBSAN
 

xen/arch/x86/include/asm/flushtlb.h

@@ -184,25 +184,6 @@ void flush_area_mask(const cpumask_t *mask, const void *va,
 }
 
 static inline void flush_page_to_ram(unsigned long mfn, bool sync_icache) {}
-static inline int invalidate_dcache_va_range(const void *p,
-                                             unsigned long size)
-{ return -EOPNOTSUPP; }
-static inline int clean_and_invalidate_dcache_va_range(const void *p,
-                                                       unsigned long size)
-{
-    unsigned int order = get_order_from_bytes(size);
-    /* sub-page granularity support needs to be added if necessary */
-    flush_area_local(p, FLUSH_CACHE|FLUSH_ORDER(order));
-    return 0;
-}
-static inline int clean_dcache_va_range(const void *p, unsigned long size)
-{
-    unsigned int order = get_order_from_bytes(size);
-
-    /* sub-page granularity support needs to be added if necessary */
-    flush_area_local(p, FLUSH_CACHE_WRITEBACK | FLUSH_ORDER(order));
-    return 0;
-}
 
 unsigned int guest_flush_tlb_flags(const struct domain *d);
 void guest_flush_tlb_mask(const struct domain *d, const cpumask_t *mask);

xen/common/Kconfig

@@ -35,6 +35,9 @@ config GRANT_TABLE
 
 	  If unsure, say Y.
 
+config HAS_GRANT_CACHE_FLUSH
+	bool
+
 config EVTCHN_FIFO
 	bool "Event Channel Fifo support" if EXPERT
 	default y

xen/common/grant_table.c

@@ -940,6 +940,7 @@ static void reduce_status_for_pin(struct domain *rd,
         gnttab_clear_flags(rd, clear_flags, status);
 }
 
+#ifdef CONFIG_HAS_GRANT_CACHE_FLUSH
 static struct active_grant_entry *grant_map_exists(const struct domain *ld,
                                                    struct grant_table *rgt,
                                                    mfn_t mfn,
@@ -975,6 +976,7 @@ static struct active_grant_entry *grant_map_exists(const struct domain *ld,
 
     return ERR_PTR(-EINVAL);
 }
+#endif /* CONFIG_HAS_GRANT_CACHE_FLUSH */
 
 union maptrack_node {
     struct {
@@ -3520,6 +3522,7 @@ gnttab_swap_grant_ref(XEN_GUEST_HANDLE_PARAM(gnttab_swap_grant_ref_t) uop,
     return 0;
 }
 
+#ifdef CONFIG_HAS_GRANT_CACHE_FLUSH
 static int _cache_flush(const gnttab_cache_flush_t *cflush, grant_ref_t *cur_ref)
 {
     struct domain *d, *owner;
@@ -3631,6 +3634,7 @@ gnttab_cache_flush(XEN_GUEST_HANDLE_PARAM(gnttab_cache_flush_t) uop,
 
     return 0;
 }
+#endif /* CONFIG_HAS_GRANT_CACHE_FLUSH */
 
 long do_grant_table_op(
     unsigned int cmd, XEN_GUEST_HANDLE_PARAM(void) uop, unsigned int count)
@@ -3773,6 +3777,7 @@ long do_grant_table_op(
         break;
     }
 
+#ifdef CONFIG_HAS_GRANT_CACHE_FLUSH
     case GNTTABOP_cache_flush:
     {
         XEN_GUEST_HANDLE_PARAM(gnttab_cache_flush_t) cflush =
@@ -3789,6 +3794,7 @@ long do_grant_table_op(
         }
         break;
     }
+#endif /* CONFIG_HAS_GRANT_CACHE_FLUSH */
 
     default:
         rc = -ENOSYS;