x86/pvh: Use correct size value in GDT descriptor

The limit field in a GDT descriptor is an inclusive bound, and therefore
one less than the size of the covered range.

Reviewed-by: Jason Andryuk <jason.andryuk@amd.com>
Tested-by: Jason Andryuk <jason.andryuk@amd.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Message-ID: <20241009160438.3884381-9-ardb+git@google.com>
Signed-off-by: Juergen Gross <jgross@suse.com>

Author: ardbiesheuvel

arch/x86/platform/pvh/head.S

@@ -224,7 +224,7 @@ SYM_CODE_END(pvh_start_xen)
 	.section ".init.data","aw"
 	.balign 8
 SYM_DATA_START_LOCAL(gdt)
-	.word gdt_end - gdt_start
+	.word gdt_end - gdt_start - 1
 	.long _pa(gdt_start) /* x86-64 will overwrite if relocated. */
 	.word 0
 SYM_DATA_END(gdt)