Re: [Lguest] lguest: unhandled trap - Kernel

This is a discussion on Re: [Lguest] lguest: unhandled trap - Kernel ; * Rusty Russell wrote: > On Monday 20 October 2008 12:50:09 Tiago Maluta wrote: > > --- On Sun, 10/19/08, Rusty Russell wrote: > > > > Hi, > > > > > > > > I'm using 2.6.27-05323-g26e9a39 and ...

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Thread: Re: [Lguest] lguest: unhandled trap

  1. Re: [Lguest] lguest: unhandled trap


    * Rusty Russell wrote:

    > On Monday 20 October 2008 12:50:09 Tiago Maluta wrote:
    > > --- On Sun, 10/19/08, Rusty Russell wrote:
    > > > > Hi,
    > > > >
    > > > > I'm using 2.6.27-05323-g26e9a39 and when I try to
    > > >
    > > > use lguest:
    > > > > ~#Documentation/lguest/lguest 128 vmlinux
    > > > > lguest: unhandled trap 14 at 0xc0594f6a (0xff900000)
    > > >
    > > > Yes, I found the same issue. Does this fix it for you?

    > >
    > > Yes. This code fixed the problem.

    >
    > Thanks. Ingo, can you push this?
    >
    > Subject: lguest: don't try DMI
    >
    > dmi_scan_machine breaks under lguest; this is the simplest fix (though
    > ugly). Perhaps this hurts Xen too?
    >
    > Error:
    > lguest: unhandled trap 14 at 0xc04edeae (0xffa00000)
    >
    > Signed-off-by: Rusty Russell
    >
    > diff -r 47449cd8e3d8 drivers/firmware/dmi_scan.c
    > --- a/drivers/firmware/dmi_scan.c Fri Oct 17 12:14:40 2008 +1100
    > +++ b/drivers/firmware/dmi_scan.c Fri Oct 17 20:54:30 2008 +1100
    > @@ -369,6 +369,11 @@ void __init dmi_scan_machine(void)
    > char __iomem *p, *q;
    > int rc;
    >
    > +#ifdef CONFIG_PARAVIRT
    > + if (strcmp(pv_info.name, "lguest") == 0)
    > + goto error;
    > +#endif
    > +


    hm, could you give some more background please? I'm not subscribed to
    the lguest list and the thread is not Cc:-ed to lkml (Cc:-ed it now).
    The patch looks quite ugly because it adds a special-case.

    Was the problem introduced by:

    5649b7c: x86: add DMI quirk for AMI BIOS which corrupts address 0xc000 during

    perhaps?

    i think Xen can withstand DMI scanning just fine.

    without having seen any background, my general feeling is that lguest
    should either do what Xen does and reserve the classic BIOS ranges that
    we probe - or we should make DMI scanning more robust by making sure
    real RAM ranges are never probed. (only ranges that the BIOS itself
    marks as reserved in the e820 map)

    (with exceptions for the first 4K perhaps.)

    Ingo
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  2. Re: [Lguest] lguest: unhandled trap

    Ingo Molnar wrote:
    > i think Xen can withstand DMI scanning just fine.
    >
    > without having seen any background, my general feeling is that lguest
    > should either do what Xen does and reserve the classic BIOS ranges that
    > we probe - or we should make DMI scanning more robust by making sure
    > real RAM ranges are never probed. (only ranges that the BIOS itself
    > marks as reserved in the e820 map)


    We considered doing that, but decided that there was so many other
    pieces of code around the place that assume that the ISA area is
    special, that just reserving it was the best course of action.

    J
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  3. Re: [Lguest] lguest: unhandled trap


    * Jeremy Fitzhardinge wrote:

    > Ingo Molnar wrote:
    >> i think Xen can withstand DMI scanning just fine.
    >>
    >> without having seen any background, my general feeling is that lguest
    >> should either do what Xen does and reserve the classic BIOS ranges
    >> that we probe - or we should make DMI scanning more robust by making
    >> sure real RAM ranges are never probed. (only ranges that the BIOS
    >> itself marks as reserved in the e820 map)

    >
    > We considered doing that, but decided that there was so many other
    > pieces of code around the place that assume that the ISA area is
    > special, that just reserving it was the best course of action.


    yeah - for _any_ virtual machine environment it's beneficial to look as
    much like a normal PC as possible, because normal PCs is where the code
    gets tested most.

    Nevertheless if this is the only current roadblock for lguest then i
    wouldnt find it objectionable to make DMI scanning more robust that way
    - the two are complimentary. [ With an initial transitionary period of
    generating printks and WARN()s when we try to scan general RAM areas. ]

    Ingo
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  4. Re: [Lguest] lguest: unhandled trap

    On Mon, 2008-10-20 at 09:53 +0200, Ingo Molnar wrote:
    > * Jeremy Fitzhardinge wrote:
    >
    > > Ingo Molnar wrote:
    > >> i think Xen can withstand DMI scanning just fine.
    > >>
    > >> without having seen any background, my general feeling is that lguest
    > >> should either do what Xen does and reserve the classic BIOS ranges
    > >> that we probe - or we should make DMI scanning more robust by making
    > >> sure real RAM ranges are never probed. (only ranges that the BIOS
    > >> itself marks as reserved in the e820 map)

    > >
    > > We considered doing that, but decided that there was so many other
    > > pieces of code around the place that assume that the ISA area is
    > > special, that just reserving it was the best course of action.

    >
    > yeah - for _any_ virtual machine environment it's beneficial to look as
    > much like a normal PC as possible, because normal PCs is where the code
    > gets tested most.
    >
    > Nevertheless if this is the only current roadblock for lguest then i
    > wouldnt find it objectionable to make DMI scanning more robust that way
    > - the two are complimentary. [ With an initial transitionary period of
    > generating printks and WARN()s when we try to scan general RAM areas. ]


    Wasn't there some concern about BIOSes which don't correctly reserve
    their DMI tables? Or don't even have e820 maps? H. Peter once said:

    > It's pretty standard for 0xf0000...0x100000 to be marked RESERVED in
    > E820 on real hardware (including the system I'm typing on right now.)
    > It is so marked to indicate that hardware cannot be mapped into that
    > space. However, you can't rely on this fact -- heck, you can't rely on
    > E820 even existing on a real machine. I have specimens of real-life
    > machines that go both ways.


    Ian.


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  5. Re: [Lguest] lguest: unhandled trap


    * Ian Campbell wrote:

    > > Nevertheless if this is the only current roadblock for lguest then i
    > > wouldnt find it objectionable to make DMI scanning more robust that
    > > way - the two are complimentary. [ With an initial transitionary
    > > period of generating printks and WARN()s when we try to scan general
    > > RAM areas. ]

    >
    > Wasn't there some concern about BIOSes which don't correctly reserve
    > their DMI tables? Or don't even have e820 maps? H. Peter once said:
    >
    > > It's pretty standard for 0xf0000...0x100000 to be marked RESERVED in
    > > E820 on real hardware (including the system I'm typing on right
    > > now.) It is so marked to indicate that hardware cannot be mapped
    > > into that space. However, you can't rely on this fact -- heck, you
    > > can't rely on E820 even existing on a real machine. I have
    > > specimens of real-life machines that go both ways.


    yes, that's a real concern, hence i suggested the printks and WARN()s to
    map such cases. And note that such problems are only an issue if it
    actually disables an essential DMI quirk. It's fair to say that if a box
    needs a DMI quirk to function properly that we can expect the BIOS to at
    least have a minimally correct memory map.

    Ingo
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  6. Re: [Lguest] lguest: unhandled trap

    Ian Campbell wrote:
    >
    > Wasn't there some concern about BIOSes which don't correctly reserve
    > their DMI tables? Or don't even have e820 maps? H. Peter once said:
    >
    >> It's pretty standard for 0xf0000...0x100000 to be marked RESERVED in
    >> E820 on real hardware (including the system I'm typing on right now.)
    >> It is so marked to indicate that hardware cannot be mapped into that
    >> space. However, you can't rely on this fact -- heck, you can't rely on
    >> E820 even existing on a real machine. I have specimens of real-life
    >> machines that go both ways.

    >


    Not only that, but the ACPI spec states explicitly that the ISA magic
    areas should be handled without relying on E820.

    -hpa
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  7. Re: [Lguest] lguest: unhandled trap

    On Monday 20 October 2008 18:22:36 Ingo Molnar wrote:
    > * Rusty Russell wrote:
    > > On Monday 20 October 2008 12:50:09 Tiago Maluta wrote:
    > > > --- On Sun, 10/19/08, Rusty Russell wrote:
    > > > > > Hi,
    > > > > >
    > > > > > I'm using 2.6.27-05323-g26e9a39 and when I try to
    > > > >
    > > > > use lguest:
    > > > > > ~#Documentation/lguest/lguest 128 vmlinux
    > > > > > lguest: unhandled trap 14 at 0xc0594f6a (0xff900000)
    > > > >
    > > > > Yes, I found the same issue. Does this fix it for you?
    > > >
    > > > Yes. This code fixed the problem.

    > >
    > > Thanks. Ingo, can you push this?
    > >
    > > Subject: lguest: don't try DMI
    > >
    > > dmi_scan_machine breaks under lguest; this is the simplest fix (though
    > > ugly). Perhaps this hurts Xen too?
    > >
    > > Error:
    > > lguest: unhandled trap 14 at 0xc04edeae (0xffa00000)
    > >
    > > Signed-off-by: Rusty Russell
    > >
    > > diff -r 47449cd8e3d8 drivers/firmware/dmi_scan.c
    > > --- a/drivers/firmware/dmi_scan.c Fri Oct 17 12:14:40 2008 +1100
    > > +++ b/drivers/firmware/dmi_scan.c Fri Oct 17 20:54:30 2008 +1100
    > > @@ -369,6 +369,11 @@ void __init dmi_scan_machine(void)
    > > char __iomem *p, *q;
    > > int rc;
    > >
    > > +#ifdef CONFIG_PARAVIRT
    > > + if (strcmp(pv_info.name, "lguest") == 0)
    > > + goto error;
    > > +#endif
    > > +

    >
    > hm, could you give some more background please? I'm not subscribed to
    > the lguest list and the thread is not Cc:-ed to lkml (Cc:-ed it now).
    > The patch looks quite ugly because it adds a special-case.
    >
    > Was the problem introduced by:
    >
    > 5649b7c: x86: add DMI quirk for AMI BIOS which corrupts address 0xc000
    > during
    >
    > perhaps?
    >
    > i think Xen can withstand DMI scanning just fine.
    >
    > without having seen any background, my general feeling is that lguest
    > should either do what Xen does and reserve the classic BIOS ranges that
    > we probe - or we should make DMI scanning more robust by making sure
    > real RAM ranges are never probed. (only ranges that the BIOS itself
    > marks as reserved in the e820 map)
    >
    > (with exceptions for the first 4K perhaps.)
    >
    > Ingo


    Yes, after this discussion I'm not even sure why it's triggering: even if
    there's crap in the memory it should not fault. Digging further.

    Cheers,
    Rusty.
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  8. Re: [Lguest] lguest: unhandled trap


    * Rusty Russell wrote:

    > On Monday 20 October 2008 18:22:36 Ingo Molnar wrote:
    > > * Rusty Russell wrote:
    > > > On Monday 20 October 2008 12:50:09 Tiago Maluta wrote:
    > > > > --- On Sun, 10/19/08, Rusty Russell wrote:
    > > > > > > Hi,
    > > > > > >
    > > > > > > I'm using 2.6.27-05323-g26e9a39 and when I try to
    > > > > >
    > > > > > use lguest:
    > > > > > > ~#Documentation/lguest/lguest 128 vmlinux
    > > > > > > lguest: unhandled trap 14 at 0xc0594f6a (0xff900000)
    > > > > >
    > > > > > Yes, I found the same issue. Does this fix it for you?
    > > > >
    > > > > Yes. This code fixed the problem.
    > > >
    > > > Thanks. Ingo, can you push this?
    > > >
    > > > Subject: lguest: don't try DMI
    > > >
    > > > dmi_scan_machine breaks under lguest; this is the simplest fix (though
    > > > ugly). Perhaps this hurts Xen too?
    > > >
    > > > Error:
    > > > lguest: unhandled trap 14 at 0xc04edeae (0xffa00000)
    > > >
    > > > Signed-off-by: Rusty Russell
    > > >
    > > > diff -r 47449cd8e3d8 drivers/firmware/dmi_scan.c
    > > > --- a/drivers/firmware/dmi_scan.c Fri Oct 17 12:14:40 2008 +1100
    > > > +++ b/drivers/firmware/dmi_scan.c Fri Oct 17 20:54:30 2008 +1100
    > > > @@ -369,6 +369,11 @@ void __init dmi_scan_machine(void)
    > > > char __iomem *p, *q;
    > > > int rc;
    > > >
    > > > +#ifdef CONFIG_PARAVIRT
    > > > + if (strcmp(pv_info.name, "lguest") == 0)
    > > > + goto error;
    > > > +#endif
    > > > +

    > >
    > > hm, could you give some more background please? I'm not subscribed to
    > > the lguest list and the thread is not Cc:-ed to lkml (Cc:-ed it now).
    > > The patch looks quite ugly because it adds a special-case.
    > >
    > > Was the problem introduced by:
    > >
    > > 5649b7c: x86: add DMI quirk for AMI BIOS which corrupts address 0xc000
    > > during
    > >
    > > perhaps?
    > >
    > > i think Xen can withstand DMI scanning just fine.
    > >
    > > without having seen any background, my general feeling is that lguest
    > > should either do what Xen does and reserve the classic BIOS ranges that
    > > we probe - or we should make DMI scanning more robust by making sure
    > > real RAM ranges are never probed. (only ranges that the BIOS itself
    > > marks as reserved in the e820 map)
    > >
    > > (with exceptions for the first 4K perhaps.)
    > >
    > > Ingo

    >
    > Yes, after this discussion I'm not even sure why it's triggering: even
    > if there's crap in the memory it should not fault. Digging further.


    we could also add an x86_quirks entry to skip the particular DMI scan
    that is causing problems. Would be nice to avoid it though, and fix
    lguest if possible.

    Ingo
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