[PATCH v2 3/5] x86/pvh: Set phys_base when calling xen_prepare_pvh()

[Jason Andryuk <jason.andryuk@amd.com>]

phys_base needs to be set for __pa() to work in xen_pvh_init() when
finding the hypercall page.  Set it before calling into
xen_prepare_pvh(), which calls xen_pvh_init().  Clear it afterward to
avoid __startup_64() adding to it and creating an incorrect value.

Signed-off-by: Jason Andryuk <jason.andryuk@amd.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
---
v2:
Fix comment style
Add Juergen's R-b
s/LOAD_PHYSICAL_ADDR/_pa(pvh_start_xen)/ in case they differ
---
 arch/x86/platform/pvh/head.S | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/x86/platform/pvh/head.S b/arch/x86/platform/pvh/head.S
index ba4d0eab4436..14b4345d9bae 100644
--- a/arch/x86/platform/pvh/head.S
+++ b/arch/x86/platform/pvh/head.S
@@ -125,7 +125,20 @@ SYM_CODE_START_LOCAL(pvh_start_xen)
 	xor %edx, %edx
 	wrmsr
 
+	/*
+	 * Calculate load offset and store in phys_base.  __pa() needs
+	 * phys_base set to calculate the hypercall page in xen_pvh_init().
+	 */
+	movq %rbp, %rbx
+	subq $_pa(pvh_start_xen), %rbx
+	movq %rbx, phys_base(%rip)
 	call xen_prepare_pvh
+	/*
+	 * Clear phys_base.  __startup_64 will *add* to its value,
+	 * so reset to 0.
+	 */
+	xor  %rbx, %rbx
+	movq %rbx, phys_base(%rip)
 
 	/* startup_64 expects boot_params in %rsi. */
 	lea pvh_bootparams(%rip), %rsi
-- 
2.34.1