Re: [Xen-ia64-devel] Re: [PATCH]: ptc.ga for SMP-g

[Isaku Yamahata <yamahata@xxxxxxxxxxxxx>]

On Thu, Mar 30, 2006 at 04:59:35PM +0800, Xu, Anthony wrote:

> There seems no issue, because vcpu_purge_tr_entry() only sets ->p=0.
> In some cases, this patch may cause a not-present tlb inserted into machine 
> TLB, this is harmless, when guest accesses this page, page not present fault
>  happens, and guest kernel will purge this tlb and insert a new one, there 
> are 
> a little performance penalty.
> Sine you will send IPI to flush vhpt later, why not purge this tlb as well as 
> flush vhpt.

Page not present fault is different from tlb miss fault.
So guest OS may handle them differently.
For example, suppose guest OS is Linux and a area covered by dtlb 
is from PAGE_OFFSET + 64MB. In this case Linux results in kernel panic.

ENTRY(page_not_present)
  -> page_fault()
     -> ia64_do_page_fault()
        Here Linux searches vm area but fails.
        then Linux tries exception table and fails.
        then panics.

It's very harmful.
-- 
yamahata

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