Re: Emulating LWZU Instruction for e500 powerpc

[Alexander Graf <agraf@suse.de>]

On 25.08.2011, at 04:30, Aashish Mittal wrote:

> 
> On Thu, Aug 25, 2011 at 4:04 AM, Alexander Graf <agraf@suse.de> wrote:
> 
> On 19.08.2011, at 06:45, Aashish Mittal wrote:
> 
> > Hi
> > I'm trying to emulate the lwzu instruction in e500 powerpc kvm for my project .
> > I've removed the read and write privileges from the tlb entries of guest's
> > certain pages . So when i'm trying to emulate lwzu instruction i'm getting a
> > kernel panic while mounting the guest filesystem while booting .
> >
> > attempt to access beyond end of device
> > ram0: rw=0, want=75703268, limit=262144
> >
> > To make sure that the emulation is  faulty what i'm trying to do now is at the
> > time of DATA STORAGE exit on a marked page by an lwzu instruction i'm patching
> > the next instruction with an instruction which will raise an INTERRUPT PROGRAM
> > EXCEPTION and will get trapped in kvm and then i'm reverting the old read and
> > write privileges of this page and resuming the guest so that this LWZU
> > instruction can run natively . I'm expecting the immediate next instruction to
> > raise the INTERRUPT PROGRAM EXCEPTION but all i'm getting are DATA STORAGE Exits
> > at other pages marked by me and DTLB and ITLB misses on other addresses .
> >
> > I've made sure to flush the icache after i patch using the instruction
> > flush_icache_range .
> >
> > Error Log :
> > Emulating a lwzu instruction on pc 0xc00161ac && eaddr 0xc05742f0
> > Original Instruction is 0x90e60004 at pc: 0xc00161b0
> > Modified Instruction is 0x7ce000a6 at pc: 0xc00161b0
> > Exit : Interrupt DATA STORAGE at pc 0xc000f210 on eaddr:0xc000f228 instruction:
> > 0x8085001c
> >
> > Why i'm not getting any INTERRUPT PROGRAM EXCEPTION immediately in the next
> > instruction ?
> 
> Hrm. Are you sure you're actually modifying the instruction? This looks like you're running Linux, so you could try and just put a "b ." instruction right after the instruction you're trying to patch up and examine memory from Qemu :)
> 
> 
> Alex
> 
> I checked the memory by reading the guest page at the modified instruction and it is the modified instruction . I think the reason i'm not getting the EXIT is because the icache is not getting flushed properly. 
> I'm trying to to flush the icache entries of the guest while i'm inside the host kvm . I'm trying to use flush_icache_range(pc , pc+ 4 ) where this pc  is the guest pc eaddr where i'm modifying the instruction . 
> 
> Do you have any idea how to flush the guest entries while i'm inside the host os given the guest eaddr of the address where i'm trying to patch the instruction . 

You need to do the icache flush on the effective address you were writing to, not the guest effective address :)


Alex