[PATCH 1/3] x86/boot: Drop pte_update_limit from physical relocation logic

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

This check has existed in one form or another since c/s 369bafdb1c1 "xen: Big
changes to x86 start-of-day" in 2007.  Even then, AFAICT, it wasn't necessary
because there was a clean split between the statically created entries (L3 and
higher) and the dynamically created ones (L2 and lower).

Without dissecting the myriad changes over the past 14 years, I'm pretty
certain Xen only booted by accident when l2_xenmap[0] was handled specially
and skipped the pte_update_limit check which would have left it corrupt.

Nevertheless, as of right now, all non-leaf PTEs (the first loop), and all 2M
xenmap leaf mappings (the second loop) need relocating.  They are no unused
mappings in the range, no mappings which will be encountered multiple times,
and it is unlikely that such mappings would be introduced.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
---
 xen/arch/x86/setup.c | 18 +++---------------
 1 file changed, 3 insertions(+), 15 deletions(-)

diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index c8641c227d9a..0492856292cf 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -1230,7 +1230,6 @@ void __init noreturn __start_xen(unsigned long mbi_p)
             l3_pgentry_t *pl3e;
             l2_pgentry_t *pl2e;
             int i, j, k;
-            unsigned long pte_update_limit;
 
             /* Select relocation address. */
             xen_phys_start = end - reloc_size;
@@ -1238,14 +1237,6 @@ void __init noreturn __start_xen(unsigned long mbi_p)
             bootsym(trampoline_xen_phys_start) = xen_phys_start;
 
             /*
-             * No PTEs pointing above this address are candidates for 
relocation.
-             * Due to possibility of partial overlap of the end of source image
-             * and the beginning of region for destination image some PTEs may
-             * point to addresses in range [e, e + XEN_IMG_OFFSET).
-             */
-            pte_update_limit = PFN_DOWN(e);
-
-            /*
              * Perform relocation to new physical address.
              * Before doing so we must sync static/global data with main memory
              * with a barrier(). After this we must *not* modify static/global
@@ -1267,8 +1258,7 @@ void __init noreturn __start_xen(unsigned long mbi_p)
                 {
                     /* Not present, 1GB mapping, or already relocated? */
                     if ( !(l3e_get_flags(*pl3e) & _PAGE_PRESENT) ||
-                         (l3e_get_flags(*pl3e) & _PAGE_PSE) ||
-                         (l3e_get_pfn(*pl3e) >= pte_update_limit) )
+                         (l3e_get_flags(*pl3e) & _PAGE_PSE) )
                         continue;
                     *pl3e = l3e_from_intpte(l3e_get_intpte(*pl3e) +
                                             xen_phys_start);
@@ -1277,8 +1267,7 @@ void __init noreturn __start_xen(unsigned long mbi_p)
                     {
                         /* Not present, PSE, or already relocated? */
                         if ( !(l2e_get_flags(*pl2e) & _PAGE_PRESENT) ||
-                             (l2e_get_flags(*pl2e) & _PAGE_PSE) ||
-                             (l2e_get_pfn(*pl2e) >= pte_update_limit) )
+                             (l2e_get_flags(*pl2e) & _PAGE_PSE) )
                             continue;
                         *pl2e = l2e_from_intpte(l2e_get_intpte(*pl2e) +
                                                 xen_phys_start);
@@ -1291,8 +1280,7 @@ void __init noreturn __start_xen(unsigned long mbi_p)
             for ( i = 0; i < L2_PAGETABLE_ENTRIES; i++, pl2e++ )
             {
                 if ( !(l2e_get_flags(*pl2e) & _PAGE_PRESENT) ||
-                     !(l2e_get_flags(*pl2e) & _PAGE_PSE) ||
-                     (l2e_get_pfn(*pl2e) >= pte_update_limit) )
+                     !(l2e_get_flags(*pl2e) & _PAGE_PSE) )
                     continue;
 
                 *pl2e = l2e_from_intpte(l2e_get_intpte(*pl2e) + 
xen_phys_start);
-- 
2.11.0