Revert "x86/pvh: Set phys_base when calling xen_prepare_pvh()"

This reverts commit f662b4a69e1d6c15db3354de6fc9f923417a5a10 which is
commit b464b461d27d564125db760938643374864c1b1f upstream.

It causes boot failures of domU guests, and should be reverted.

Cc: Jason Andryuk <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: Sasha Levin <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Reported-by: Marek Marczykowski-Górecki <[email protected]>
Link: https://lore.kernel.org/r/Z1l6XbHP6BTTZSwr@mail-itl
Signed-off-by: Greg Kroah-Hartman <[email protected]>

arch/x86/platform/pvh/head.S

@@ -100,20 +100,7 @@ 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. */
 	mov $_pa(pvh_bootparams), %rsi