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Re: [Xen-devel] 32bit PAE PV guest on 64bit hypervisor

To: mukesh.rathor@xxxxxxxxxx
Subject: Re: [Xen-devel] 32bit PAE PV guest on 64bit hypervisor
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Tue, 14 Apr 2009 08:59:47 -0700
Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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Mukesh Rathor wrote:
Hi,

Been chasing down this message from guest boot:

(XEN) mm.c:1841:d1 Error pfn 7f36a: rd=ffff8300cea28080,
od=0000000000000000, caf=00000000, taf=0000000000000000
(XEN) mm.c:730:d1 Error getting mfn 7f36a (pfn 5555555555555555) from L1
entry 000000007f36a025 for dom1
(XEN) mm.c:3700:d1 ptwr_emulate: fixing up invalid PAE PTE
000000007f36a025

Firstly, on a >64GB system, looks like a 32bit guest can get mfn above 64G.

The above msg comes when the PV guest tries to do WP check. To that end,
it does set_pte for mapping a (some swapper) temp page in test_wp_bit():

__set_fixmap(FIX_WP_TEST, __pa_symbol(&swapper_pg_dir), PAGE_READONLY);
      boot_cpu_data.wp_works_ok = do_test_wp_bit();
      clear_fixmap(FIX_WP_TEST);

...
/* use writable pagetables */
static inline void set_pte(pte_t *ptep, pte_t pte)
{
        ptep->pte_high = pte.pte_high;
    smp_wmb();
    ptep->pte_low = pte.pte_low;
}

What kernel version is this?

   J

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