[PATCH 02/14] x86/xstate: Create map/unmap primitives for xsave areas

[Alejandro Vallejo <alejandro.vallejo@cloud.com>]

Add infrastructure to simplify ASI handling. With ASI in the picture
we'll have several different means of accessing the XSAVE area of a
given vCPU, depending on whether a domain is covered by ASI or not and
whether the vCPU is question is scheduled on the current pCPU or not.

Having these complexities exposed at the call sites becomes unwieldy
very fast. These wrappers are intended to be used in a similar way to
map_domain_page() and unmap_domain_page(); The map operation will
dispatch the appropriate pointer for each case in a future patch, while
unmap will remain a no-op where no unmap is required (e.g: when there's
no ASI) and remove the transient maping if one was required.

Follow-up patches replace all uses of raw v->arch.xsave_area by this
mechanism in preparation to add the beforementioned dispatch logic to be
added at a later time.

Signed-off-by: Alejandro Vallejo <alejandro.vallejo@cloud.com>
---
 xen/arch/x86/include/asm/xstate.h | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/xen/arch/x86/include/asm/xstate.h b/xen/arch/x86/include/asm/xstate.h
index 07017cc4edfd..36260459667c 100644
--- a/xen/arch/x86/include/asm/xstate.h
+++ b/xen/arch/x86/include/asm/xstate.h
@@ -143,4 +143,24 @@ static inline bool xstate_all(const struct vcpu *v)
            (v->arch.xcr0_accum & XSTATE_LAZY & ~XSTATE_FP_SSE);
 }
 
+/*
+ * Fetch a pointer to the XSAVE area of a vCPU
+ *
+ * If ASI is enabled for the domain, this mapping is pCPU-local.
+ *
+ * @param v Owner of the XSAVE area
+ */
+#define vcpu_map_xsave_area(v) ((v)->arch.xsave_area)
+
+/*
+ * Drops the XSAVE area of a vCPU and nullifies its pointer on exit.
+ *
+ * If ASI is enabled and v is not the currently scheduled vCPU then the
+ * per-pCPU mapping is removed from the address space.
+ *
+ * @param v           vCPU logically owning xsave_area
+ * @param xsave_area  XSAVE blob of v
+ */
+#define vcpu_unmap_xsave_area(v, x) ({ (x) = NULL; })
+
 #endif /* __ASM_XSTATE_H */
-- 
2.47.0