[Xen-changelog] [xen staging] xen/arm: mm: Allow generic xen page-tables helpers to be called early

[patchbot@xxxxxxx]

commit 8d4f1b8878e096edff74b0d270ac53b5c697e311
Author:     Julien Grall <julien.grall@xxxxxxx>
AuthorDate: Tue Oct 15 20:16:10 2019 +0100
Commit:     Julien Grall <julien.grall@xxxxxxx>
CommitDate: Tue Oct 22 17:57:51 2019 +0100

    xen/arm: mm: Allow generic xen page-tables helpers to be called early
    
    The current implementations of xen_{map, unmap}_table() expect
    {map, unmap}_domain_page() to be usable. Those helpers are used to
    map/unmap page tables while update Xen page-tables.
    
    Since commit 022387ee1a "xen/arm: mm: Don't open-code Xen PT update in
    {set, clear}_fixmap()", setup_fixmap() will make use of the helpers
    mentioned above. When booting Xen using GRUB, setup_fixmap() may be used
    before map_domain_page() can be called. This will result to data abort:
    
    (XEN) Data Abort Trap. Syndrome=0x5
    (XEN) CPU0: Unexpected Trap: Data Abort
    
    [...]
    
    (XEN) Xen call trace:
    (XEN)    [<000000000025ab6c>] mm.c#xen_pt_update+0x2b4/0x59c (PC)
    (XEN)    [<000000000025ab20>] mm.c#xen_pt_update+0x268/0x59c (LR)
    (XEN)    [<000000000025ae70>] set_fixmap+0x1c/0x2c
    (XEN)    [<00000000002a9c98>] copy_from_paddr+0x7c/0xdc
    (XEN)    [<00000000002a4ae0>] has_xsm_magic+0x18/0x34
    (XEN)    [<00000000002a5b5c>] bootfdt.c#early_scan_node+0x398/0x560
    (XEN)    [<00000000002a5de0>] device_tree_for_each_node+0xbc/0x144
    (XEN)    [<00000000002a5ed4>] boot_fdt_info+0x6c/0x260
    (XEN)    [<00000000002ac0d0>] start_xen+0x108/0xc74
    (XEN)    [<000000000020044c>] arm64/head.o#paging+0x60/0x88
    
    During early boot, the page tables are either statically allocated in
    Xen binary or allocated via alloc_boot_pages().
    
    For statically allocated page-tables, they will already be mapped as
    part of Xen binary. So we can easily find the virtual address.
    
    For dynamically allocated page-tables, we need to rely
    map_domain_page() to be functionally working.
    
    For arm32, the call will be usable much before page can be dynamically
    allocated (see setup_pagetables()). For arm64, the call will be usable
    after setup_xenheap_mappings().
    
    In both cases, memory are given to the boot allocator afterwards. So we
    can rely on map_domain_page() for mapping page tables allocated
    dynamically.
    
    The helpers xen_{map, unmap}_table() are now updated to take into
    account the case where page-tables are part of Xen binary.
    
    Fixes: 022387ee1a ('xen/arm: mm: Don't open-code Xen PT update in {set, 
clear}_fixmap()')
    Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
    Release-acked-by: Juergen Gross <jgross@xxxxxxxx>
    Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
---
 xen/arch/arm/mm.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index 01891293b8..4d6c971f37 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -973,11 +973,41 @@ static int create_xen_table(lpae_t *entry)
 
 static lpae_t *xen_map_table(mfn_t mfn)
 {
+    /*
+     * We may require to map the page table before map_domain_page() is
+     * useable. The requirements here is it must be useable as soon as
+     * page-tables are allocated dynamically via alloc_boot_pages().
+     *
+     * We need to do the check on physical address rather than virtual
+     * address to avoid truncation on Arm32. Therefore is_kernel() cannot
+     * be used.
+     */
+    if ( system_state == SYS_STATE_early_boot )
+    {
+        if ( is_xen_fixed_mfn(mfn) )
+        {
+            /*
+             * It is fine to demote the type because the size of Xen
+             * will always fit in vaddr_t.
+             */
+            vaddr_t offset = mfn_to_maddr(mfn) - virt_to_maddr(&_start);
+
+            return (lpae_t *)(XEN_VIRT_START + offset);
+        }
+    }
+
     return map_domain_page(mfn);
 }
 
 static void xen_unmap_table(const lpae_t *table)
 {
+    /*
+     * During early boot, xen_map_table() will not use map_domain_page()
+     * for page-tables residing in Xen binary. So skip the unmap part.
+     */
+    if ( system_state == SYS_STATE_early_boot && is_kernel(table) )
+        return;
+
     unmap_domain_page(table);
 }
 
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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