[RFC PATCH 04/12] x86/xen: Introduce new function to map HYPERVISOR_shared_info on Resume

[Anchal Agarwal <anchalag@amazon.com>]

Introduce a small function which re-uses shared page's PA allocated
during guest initialization time in reserve_shared_info() and not
allocate new page during resume flow.
It also  does the mapping of shared_info_page by calling
xen_hvm_init_shared_info() to use the function.

Signed-off-by: Anchal Agarwal <anchalag@amazon.com>
Reviewed-by: Sebastian Biemueller <sbiemue@amazon.com>
Reviewed-by: Munehisa Kamata <kamatam@amazon.com>
Reviewed-by: Eduardo Valentin <eduval@amazon.com>
CR: https://cr.amazon.com/r/8273203/
---
 arch/x86/xen/enlighten_hvm.c | 7 +++++++
 arch/x86/xen/xen-ops.h       | 1 +
 2 files changed, 8 insertions(+)

diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
index 754d5391d9fa..2c4bcf92a90a 100644
--- a/arch/x86/xen/enlighten_hvm.c
+++ b/arch/x86/xen/enlighten_hvm.c
@@ -24,6 +24,13 @@
 
 static unsigned long shared_info_pfn;
 
+void xen_hvm_map_shared_info(void)
+{
+	xen_hvm_init_shared_info();
+	if (shared_info_pfn)
+		HYPERVISOR_shared_info = __va(PFN_PHYS(shared_info_pfn));
+}
+
 void xen_hvm_init_shared_info(void)
 {
 	struct xen_add_to_physmap xatp;
diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
index f377e1820c6c..94c8a009ab35 100644
--- a/arch/x86/xen/xen-ops.h
+++ b/arch/x86/xen/xen-ops.h
@@ -58,6 +58,7 @@ void xen_enable_syscall(void);
 void xen_vcpu_restore(void);
 
 void xen_callback_vector(void);
+void xen_hvm_map_shared_info(void);
 void xen_hvm_init_shared_info(void);
 void xen_unplug_emulated_devices(void);
 
-- 
2.14.3