----- Original Message -----
> On Fri, Mar 16, 2018 at 04:33:41PM -0400, Dave Anderson wrote:
> >
> > Hi Sergio,
> >
> > A few initial comments/questions/concerns about this patch...
> >
> > > diff --git a/diskdump.c b/diskdump.c
> > > index b08a46c..1ec4bcf 100644
> > > --- a/diskdump.c
> > > +++ b/diskdump.c
> > > @@ -56,6 +56,7 @@ struct diskdump_data {
> > > void **nt_prstatus_percpu;
> > > uint num_prstatus_notes;
> > > void **nt_qemu_percpu;
> > > + void **nt_qemucs_percpu;
> > > uint num_qemu_notes;
> > >
> > > /* page cache */
> > > @@ -72,6 +73,7 @@ struct diskdump_data {
> > > ulong *valid_pages;
> > > ulong accesses;
> > > ulong snapshot_task;
> > > + ulong kaslr_phys_base;
> > > };
> >
> > Generally speaking, there already is an sd->phys_base, and you've
> > added an nd->phys_base, but I don't understand why you also added
> > a new dd->kaslr_phys_base member and new diskdump_kaslr_phys_base()
> > function? Is there any reason that you can't continue to use the
> > currently-existing dd->sub_header_kdump->phys_base member and the
> > diskdump_phys_base() function? I just find the concept of a
> > "kaslr_phys_base" confusing, i.e., as if there are two different
> > types of phys_base in the kernel. Can you please try to utilize
> > the existing member and function?
> >
> > Also related, your diskdump_kaslr_phys_base() and kdump_phys_base()
> > functions
> > don't account for (return FALSE) with a legitimate phys_base value of 0.
> > In fact I have a sample RHEL7 ELF vmcore generated by virsh dump which
> > has a phys_base of 0. More on that below...
>
> Both of these are the consequence of trying to avoid changing the current
> SADUMP's implementation while keeping NETDUMP's and DISKDUMP's as similar as
> possible.
>
> But if there's no problem in changing SADUMP's, I would change the setters to
> succeed unconditionally, and remove the "if (base->phys_base)" check from the
> getters. This would make them semantically equivalent to current's
> "diskdump_phys_base", which is the main reason I've added kaslr_phys_base,
> allowing me to use the existing dd->sub_header_kdump->phys_base.
No, I would leave the SADUMP implementation as it is. First, I don't maintain it,
and secondly, apparently the hardware that it runs on always has a non-zero
phys_base? I really don't know. The sadump maintainers will be ACK'ing this
patchset as well, so I will leave it up to them.
But diskdump_phys_base() and kdump_phys_base() -- as long as the dumpfile type is
verified -- should return whatever is there, including zero, regardless whether
it is the initialization value or set legitimately. The subsequent call to
x86_64_virt_phys_base() will either verify it, or if lucky, calculate it += 16MB.
Make sense?
>
> > > diff --git a/kaslr_helper.c b/kaslr_helper.c
> > > index 1079863..5b71e3e 100644
> > > --- a/kaslr_helper.c
> > > +++ b/kaslr_helper.c
> > > @@ -386,6 +386,9 @@ calc_kaslr_offset(ulong *kaslr_offset, ulong
> > > *phys_base)
> > > if (KDUMP_DUMPFILE()) {
> > > idtr = kdump_get_idtr();
> > > cr3 = kdump_get_cr3();
> > > + } else if (DISKDUMP_DUMPFILE()) {
> > > + idtr = diskdump_get_idtr();
> > > + cr3 = diskdump_get_cr3();
> >
> > All 4 of these new functions above can fail and return 0. Probably
> > unlikely, but shouldn't there be a FALSE return if either one is 0,
> > rather than continuing and using them?
>
> Again, I was trying to keep in sync with current SADUMP's implementation.
Yeah, you're right -- looking at the current sadump implementation, it looks
like even though its get_sadump_smram_cpu_state_any() function can return FALSE,
sadump_calc_kaslr_offset() doesn't bother to check it.
> Otherwise, I'd prefer implementing a single function like this:
>
> int [diskdump|kdump|sadump]_get_idtr_cr3(uint64_t *idtr, uint64_t *cr3);
>
> That would allow me to write some like:
>
> if ((KDUMP_DUMPFILE() && !kdump_get_idtr_cr3(&idtr, &cr3)) ||
> (DISKDUMP_DUMPFILE() && !diskdump_get_idtr_cr3(&idtr, &cr3))) {
> return FALSE;
> }
>
> What do you think?
Looks OK -- but since your kdump_get_idtr() is identical to diskdump_get_idtr(),
and kdump_get_cr3() is identical to diskdump_get_cr3(), why can't the 4 functions
be merged into a single function, and put in the new kaslr_helper.c? I understand
why the two get_qemucpustate() functions exist.
>
> > > } else {
> > > return FALSE;
> > > }
> >
> > > diff --git a/x86_64.c b/x86_64.c
> > > index ed5985a..3c492e4 100644
> > > --- a/x86_64.c
> > > +++ b/x86_64.c
> > > @@ -6632,8 +6632,15 @@ x86_64_calc_phys_base(void)
> > > * Get relocation value from whatever dumpfile format is being used.
> > > */
> > >
> > > - if (QEMU_MEM_DUMP_NO_VMCOREINFO() && KDUMP_DUMPFILE()) {
> > > - if (kdump_phys_base(&phys_base)) {
> > > + if (QEMU_MEM_DUMP_NO_VMCOREINFO()) {
> > > + int ret;
> > > +
> > > + if (KDUMP_DUMPFILE())
> > > + ret = kdump_phys_base(&phys_base);
> > > + else if (DISKDUMP_DUMPFILE())
> > > + ret = diskdump_kaslr_phys_base(&phys_base);
> > > +
> > > + if (ret) {
> > > machdep->machspec->phys_base = phys_base;
> > > if (CRASHDEBUG(1))
> > > fprintf(fp, "kdump-novmci: phys base: %lx\n",
> > > --
> > > 2.14.3
> >
> > This is where the "0 phys_base" issue comes into play. I think the section
> > above should do the same thing as the following "if (DISKDUMP_DUMPFILE())"
> > does, where diskump_phys_base() is only concerned if the dumpfile itself
> > is valid. It may return 0 as a phys_base, and that's OK, because it
> > unconditionally calls x86_64_virt_phys_base() -- which serves a dual
> > purpose, either to:
> >
> > (1) verify it, or
> > (2) if it's bogus, it checks whether plus-or-minus 16MB works.
>
> After switching to using dd->sub_header_kdump->phys_base, do you think we can
> just leave QEMU_MEM_DUMP_COMPRESSED to be dealt by the DISKDUMP_DUMPFILE
> section, and add another equivalent one for QEMU_MEM_DUMP_ELF && !VMCOREINFO?
I would keep the QEMU_MEM_DUMP_NO_VMCOREINFO() section where it is, because it
still potentially calls your new kdump_phys_base().
Thanks,
Dave
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