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SubjectRe: [PATCH v3 1/3] x86/ldt: Make modify_ldt synchronous


On 07/22/2015 06:20 PM, Boris Ostrovsky wrote:
> On 07/22/2015 03:23 PM, Andy Lutomirski wrote:
>>
>> + error = -ENOMEM;
>> + new_ldt = alloc_ldt_struct(newsize);
>> + if (!new_ldt)
>> goto out_unlock;
>> - }
>> - fill_ldt(&ldt, &ldt_info);
>> - if (oldmode)
>> - ldt.avl = 0;
>> + if (old_ldt) {
>> + memcpy(new_ldt->entries, old_ldt->entries,
>> + oldsize * LDT_ENTRY_SIZE);
>> + }
>> + memset(new_ldt->entries + oldsize * LDT_ENTRY_SIZE, 0,
>> + (newsize - oldsize) * LDT_ENTRY_SIZE);
>
> We need to zero out full page (probably better in alloc_ldt_struct()
> with vmzalloc/__GFP_ZERO) --- Xen checks whole page that is assigned
> to G/LDT and gets unhappy if an invalid descriptor is found there.
>
> This fixes one problem. There is something else that Xen gets upset
> about, I haven't figured what it is yet (and I am out tomorrow so it
> may need to wait until Friday).
>


What I thought was another problem turned out not to be one so both 64-
and 32-bit tests passed on 64-bit PV (when allocated LDT is zeroed out)

However, on 32-bit kernel the test is failing multicpu test, I don't
know yet what it is.

-boris




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