Another NaT question...
>I recall that some time ago (around the time of the merge)
>you submitted some patches related to fixing ar.unat saving
>and restoring.
Another part of your earlier patch was a change in
ia64_handle_reflection. I still periodically get the
message:
NaT fault... attempting to handle as privop
Since your latest fix, Tony's regcheck tool no longer
reports ar.unat as being saved/restored incorrectly.
I was hoping that the above message would go away also,
but it has not. I see it a couple times at boot and
a couple times for every linux compile (at the end so
it is probably the linker or some other link-related
tool). I have also seen programs segfault after printing
this message. So I went to look at the Xen/ia64 code where
this is printed.
It doesn't look right to me. There are two issues:
1) Your patch added a "return"... I think this means that
NaT faults will never get reflected to a guest (even
Register NaT Consumption faults).
2) Since a Instruction NaTPage Consumption fault has higher
priority than a Privileged Operation fault, I think the
original printf/priv_emulate code was intended to catch
this case and properly emulate a privileged instruction
on a NaTPage. I think it may also be necessary if a Data
NaTPage Consumption fault is incurred when the privop
emulation code fetches the instruction. (The code in
ia64_handle_reflection should probably check the ISR to
avoid calling priv_emulate for other kinds of NaT
Consumption though.)
You know more about NaT's than I do... could you recheck
this code in ia64_handle_reflection please? Do you have
any test code that provokes any of these NaT faults?
Thanks.
Dan
> -----Original Message-----
> From: Xu, Anthony [mailto:anthony.xu@xxxxxxxxx]
> Sent: Friday, November 04, 2005 12:10 AM
> To: Magenheimer, Dan (HP Labs Fort Collins)
> Cc: xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
> Subject: RE: ar.unat[patch] fixed this ar.uant issue.[patch]
> fixed ar.unat save/restore issue
>
> >I am curious about the use of B1NATS in the code
> >around this patch. Under what circumstances does
> >this get set/used?
>
> 1. emulate bsw1, bsw0
> 2. emulate rfi.
> 3. inject fault to guest.
>
> There is similar unat code in
> >fast_tick (default off) and fast_reflect (default on)
> >and I am wondering if similar unat changes are needed
> >and whether it is now OK to turn on HANDLE_AR_UNAT
> >(which is now default off).
> You are right, in above two cases you should also save
> ar.unat to XSI_B1NATS_OFS after spilling the guest bank1to
> share page. I had handled all this in C code. I didn't look
> into fast hypercall code, It's hard to read due to I am not
> good at assembly code. The principle of handling ar.unat is
> obvious; every time you spill banking register you must save
> corresponding ar.unat after it, every time you fill banking
> register you must restore corresponding ar.unat before it.
>
> We don't need to clear all guest b0 registers and their's nat
> bit. Because r16~r23 are preserved regs and r24~r31 are
> scratch regs, we only need to restore r16~r23 rather than
> clear r16~r23 to 0.
>
> Next time you enable some functions like hyper_ssm_i, when
> you save bank1 regs you should also save bank1 unat.
>
> Below patch enables HANDLE_AR_UNAT.
>
>
>
> Signed-off-by Anthony Xu <Anthony.xu@xxxxxxxxx>
>
> Thanks,
> Anthony.
>
>
>
>
> >-----Original Message-----
> >From: Magenheimer, Dan (HP Labs Fort Collins)
> [mailto:dan.magenheimer@xxxxxx]
> >Sent: 2005年11月3日 22:42
> >To: Xu, Anthony
> >Cc: xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
> >Subject: RE: ar.unat[patch] fixed this ar.uant issue.
> >
> >Hi Anthony --
> >
> >I am curious about the use of B1NATS in the code
> >around this patch. Under what circumstances does
> >this get set/used? There is similar unat code in
> >fast_tick (default off) and fast_reflect (default on)
> >and I am wondering if similar unat changes are needed
> >and whether it is now OK to turn on HANDLE_AR_UNAT
> >(which is now default off).
> >
> >Thanks,
> >Dan
> >
> >> -----Original Message-----
> >> From: Xu, Anthony [mailto:anthony.xu@xxxxxxxxx]
> >> Sent: Thursday, November 03, 2005 1:08 AM
> >> To: Magenheimer, Dan (HP Labs Fort Collins)
> >> Cc: xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
> >> Subject: RE: ar.unat[patch] fixed this ar.uant issue.
> >>
> >> Dan,
> >> Last time, I used ar.unat register to restore guest general
> >> register nat bit in hyper_rfi function for eliminating nat
> >> bit consumption fault,but not restored ar.unat.
> >>
> >> Signed-off-by Anthony Xu <Anthony.xu@xxxxxxxxx>
> >>
> >> Thanks,
> >> Anthony.
> >>
> >>
> >>
> >>
> >> >-----Original Message-----
> >> >From: Magenheimer, Dan (HP Labs Fort Collins)
> >> [mailto:dan.magenheimer@xxxxxx]
> >> >Sent: 2005年11月3日 11:54
> >> >To: Xu, Anthony
> >> >Cc: xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
> >> >Subject: RE: ar.unat
> >> >
> >> >> I can take a look at this, please send me regcheck utilty.
> >> >>
> >> >>
> >> >> Thanks
> >> >> Anthony
> >> >
> >> >Great, thanks! Here's where I got Tony's regcheck tool. If
> >> >it's not still there, perhaps Tony can post it.
> >> >
> >> >By the way, if anyone tries this on a domU, Matt Chapman
> >> >has a pending fix that resolves a FP save/restore issue.
> >> >
> >> >Thanks,
> >> >Dan
> >> >
> >> >> -----Original Message-----
> >> >> From: linux-ia64-owner@xxxxxxxxxxxxxxx
> >> >> [mailto:linux-ia64-owner@xxxxxxxxxxxxxxx] On Behalf Of
> Luck, Tony
> >> >> Sent: Tuesday, March 01, 2005 4:33 PM
> >> >> To: linux-ia64@xxxxxxxxxxxxxxx
> >> >> Subject: RE: [patch 2.6.11-rc3-bk4] Correctly dereference
> >> >> ia64_mca_data
> >> >>
> >> >> Back on February 9th, I wrote:
> >> >> >I wrote a test program that loads up random values
> into registers
> >> >> >(just r1-r31, a bunch of stacked registers, and
> f2-f127 for now)
> >> >> >and then checks that all the registers haven't changed value a
> >> >> >few thousand times, before reloading with a new set of random
> >> >> >values.
> >> >>
> >> >> A few people asked whether I could post the program ... it took
> >> >> a while to get sign-off ... but that gave me time to
> add "branch",
> >> >> "predicate" and half a dozen "application" registers to the mix,
> >> >> plus make it print the name of the register that was
> nuked (instead
> >> >> of a number that required manual translation).
> >> >>
> >> >> I've tested it by using a debugger to zap one of each class
> >> >> of register
> >> >> that is being monitored to check that it works.
> >> >>
> >> >>
> http://www.kernel.org/pub/linux/kernel/people/aegl/ia64regcheck.tgz
> >> >>
> >> >> Usage ... compile, and run a few copies. If they all
> >> "exit(0)" (which
> >> >> may take a couple of days) the test passed. Otherwise you
> >> should see
> >> >> the name of the register printed to stderr, and exit code 1.
> >> >>
> >> >> Apart from the MCA case, I haven't seen it report a problem
> >> >> yet ... but
> >> >> I've only run a few hours.
> >> >>
> >> >> -Tony
> >>
>
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