Re: [Xen-devel] Mapping page table pages read-only

[Simon Kagstrom <simon.kagstrom@xxxxxx>]

At Tue, 02 May 2006 11:10:21 +0200,
Simon Kagstrom wrote:
> 
>    HYPERVISOR_update_va_mapping((unsigned long)page,
>                                 (pte_t){(unsigned long)phys_to_machine(page)},
>                               PRESENT);
> 
> , being careful to only set bit 0 (PRESENT), which should make the
> page read-only. If I do this, however, I get an access violation on
> access of the page table page. Can anyone tell me what I do wrong
> here?

Oh dear. My fault.

For reference, the error was that I placed the page flags in the
update_va_mapping flags field, whereas they should be in actual entry,
i.e.,

    HYPERVISOR_update_va_mapping((unsigned long)page,
                                 (pte_t){(unsigned long)phys_to_machine(page) | 
FLAGS},
                                 0);

works much better. On to the next problem!


// Simon

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