RE: [Xen-devel] Switching from writeable pagetabletoshadowlog-dirtyat runtime

["Nakajima, Jun" <jun.nakajima@xxxxxxxxx>]

Ian Pratt wrote:
>> We found that in 32-bit code, the shadow_fault() do one more thing
>> than 64-bit code. The following code in file shadow32.c checks the
>> L1 page table with RW bit removed and make the shadow with RW bit, it
>> does not inject the fault to guest.
>> Does this is a work-around for switch from writable pagetable to
>> shadow mode enable? Does this code makes sense to the writeable
>> pagetable, and then may be one reason that 32bit log-dirty code can
>> work? 
> 
> Yep, the code you highlight is in shadow32 to support writable
> pagetable emulation when in shadow mode.
> 
> My original shadow mode implementation didn't need special case code
> to handle writable pagetables as the shadow fault handler was called
> after the writeable pagetable handler in the main page fault handler:
> the writeable pagetable fault was handled but then eecution was
> allowed to drop through into the shadow fault handler, propagating
> the change into the shadow pagetable without having to take another
> fault. It may be possible to do something similar to remove the
> special case, but I'm less familiar with the current code.
> 
> Ian

So, let's add the code to shadow.c and continue on debugging. 

Jun
---
Intel Open Source Technology Center

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