From: Cornelia Huck <cohuck@redhat.com>
To: David Hildenbrand <david@redhat.com>
Cc: Thomas Huth <thuth@redhat.com>,
Janosch Frank <frankja@linux.ibm.com>,
qemu-devel@nongnu.org, Ilya Leoshkevich <iii@linux.ibm.com>,
Halil Pasic <pasic@linux.ibm.com>,
Christian Borntraeger <borntraeger@de.ibm.com>,
qemu-s390x@nongnu.org, Richard Henderson <rth@twiddle.net>
Subject: Re: [Qemu-devel] [PATCH-for-4.2 v1 1/9] s390x/mmu: Better ASC selection in s390_cpu_get_phys_page_debug()
Date: Mon, 12 Aug 2019 15:58:17 +0200 [thread overview]
Message-ID: <20190812155817.2edb133c.cohuck@redhat.com> (raw)
In-Reply-To: <94fc262e-b8d7-df09-1461-f10a9874d954@redhat.com>
On Mon, 12 Aug 2019 15:45:25 +0200
David Hildenbrand <david@redhat.com> wrote:
> On 12.08.19 15:40, Cornelia Huck wrote:
> > On Mon, 12 Aug 2019 09:52:56 +0200
> > David Hildenbrand <david@redhat.com> wrote:
> >
> >> On 12.08.19 09:12, Thomas Huth wrote:
> >>> On 8/5/19 5:29 PM, David Hildenbrand wrote:
> >>>> Let's select the ASC before calling the function and use MMU_DATA_LOAD.
> >>>> This is a preparation to:
> >>>> - Remove the ASC magic depending on the access mode from mmu_translate
> >>>> - Implement IEP support, where we could run into access exceptions
> >>>> trying to fetch instructions
> >>>>
> >>>> Signed-off-by: David Hildenbrand <david@redhat.com>
> >>>> ---
> >>>> target/s390x/helper.c | 10 +++++++++-
> >>>> 1 file changed, 9 insertions(+), 1 deletion(-)
> >>>>
> >>>> diff --git a/target/s390x/helper.c b/target/s390x/helper.c
> >>>> index 13ae9909ad..08166558a0 100644
> >>>> --- a/target/s390x/helper.c
> >>>> +++ b/target/s390x/helper.c
> >>>> @@ -58,7 +58,15 @@ hwaddr s390_cpu_get_phys_page_debug(CPUState *cs, vaddr vaddr)
> >>>> vaddr &= 0x7fffffff;
> >>>> }
> >>>>
> >>>> - if (mmu_translate(env, vaddr, MMU_INST_FETCH, asc, &raddr, &prot, false)) {
> >>>> + /*
> >>>> + * We want to read the code, however, not run into access exceptions
> >>>
> >>> Is this really a safe assumption here that we always use this to
> >>> translate code addresses and not data addresses? ... I don't think so.
> >>> For example with the "gva2gpa" HMP command, I'd rather expect that it
> >>> also works with the secondary space mode...?
> >>
> >> Well, it's what current code does. I am not changing that behavior.
> >
> > Agreed, that is not actively breaking something.
> >
> >>
> >> While it is in general broken to have a single interface to debug
> >> code+data (which is only a problem on s390x), it makes a lot of sense if
> >> you think about single-stepping through disassembled code using the
> >> gdbstub. Or dumping code where you crashed.
> >
> > What about the memsave interface?
>
> I guess the same problem:
>
> "save to disk virtual memory dump starting at @var{addr} of size
> @var{size}" - which virtual memory (code vs. data)? These old interface
> are really x86 specific (meaning: it made sense this way for x86)
So, the general verdict is "gnarly interface, but at least not broken
for Linux guests", I guess.
>
> I'd like to note that if our KVM guest is in AR mode, we would now no
> longer be able to crash it :) (well, a nice side-effect of instruction
> fetches not going via AR mode).
Heh :)
Q: What do we need to consider beyond Linux guests? Probably not much,
given that they would be broken already...
next prev parent reply other threads:[~2019-08-12 13:58 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-05 15:29 [Qemu-devel] [PATCH-for-4.2 v1 0/9] s390x: MMU changes and extensions David Hildenbrand
2019-08-05 15:29 ` [Qemu-devel] [PATCH-for-4.2 v1 1/9] s390x/mmu: Better ASC selection in s390_cpu_get_phys_page_debug() David Hildenbrand
2019-08-08 12:57 ` Cornelia Huck
2019-08-08 13:02 ` David Hildenbrand
2019-08-12 7:12 ` Thomas Huth
2019-08-12 7:52 ` David Hildenbrand
2019-08-12 13:40 ` Cornelia Huck
2019-08-12 13:45 ` David Hildenbrand
2019-08-12 13:58 ` Cornelia Huck [this message]
2019-08-12 14:14 ` David Hildenbrand
2019-08-05 15:29 ` [Qemu-devel] [PATCH-for-4.2 v1 2/9] s390x/tcg: Rework MMU selection for instruction fetches David Hildenbrand
2019-08-05 15:29 ` [Qemu-devel] [PATCH-for-4.2 v1 3/9] s390x/mmu: DAT translation rewrite David Hildenbrand
2019-08-12 7:20 ` Thomas Huth
2019-08-12 7:43 ` David Hildenbrand
2019-08-12 8:04 ` David Hildenbrand
2019-08-19 11:40 ` [Qemu-devel] [qemu-s390x] " Thomas Huth
2019-08-19 11:58 ` David Hildenbrand
2019-08-19 12:00 ` Thomas Huth
2019-08-05 15:29 ` [Qemu-devel] [PATCH-for-4.2 v1 4/9] s390x/mmu: Add EDAT2 translation support David Hildenbrand
2019-08-19 12:01 ` [Qemu-devel] [qemu-s390x] " Thomas Huth
2019-08-05 15:29 ` [Qemu-devel] [PATCH-for-4.2 v1 5/9] s390x/mmu: Implement access-exception-fetch/store-indication facility David Hildenbrand
2019-08-19 12:16 ` [Qemu-devel] [qemu-s390x] " Thomas Huth
2019-08-19 12:22 ` Thomas Huth
2019-08-19 12:26 ` David Hildenbrand
2019-08-19 12:30 ` Thomas Huth
2019-08-19 12:35 ` David Hildenbrand
2019-08-05 15:29 ` [Qemu-devel] [PATCH-for-4.2 v1 6/9] s390x/mmu: Implement enhanced suppression-on-protection facility 2 David Hildenbrand
2019-08-19 14:58 ` [Qemu-devel] [qemu-s390x] " Thomas Huth
2019-08-05 15:29 ` [Qemu-devel] [PATCH-for-4.2 v1 7/9] s390x/mmu: Implement Instruction-Execution-Protection Facility David Hildenbrand
2019-08-19 15:03 ` [Qemu-devel] [qemu-s390x] " Thomas Huth
2019-08-05 15:29 ` [Qemu-devel] [PATCH-for-4.2 v1 8/9] s390x/cpumodel: Prepare for changes of QEMU model David Hildenbrand
2019-08-13 16:02 ` Cornelia Huck
2019-08-19 15:07 ` [Qemu-devel] [qemu-s390x] " Thomas Huth
2019-08-05 15:29 ` [Qemu-devel] [PATCH-for-4.2 v1 9/9] s390x/cpumodel: Add new TCG features to QEMU cpu model David Hildenbrand
2019-08-13 16:07 ` Cornelia Huck
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