On Tue, Jun 29, 2021 at 07:07:21AM +0000, HAGIO KAZUHITO(萩尾 一仁) wrote:
> -----Original Message-----
> > > > @@ -1033,7 +1050,11 @@ arm64_calc_phys_offset(void)
> > > > ms->kimage_voffset && (sp = kernel_symbol_search("memstart_addr"))) {
> > > > if (pc->flags & PROC_KCORE) {
> > > > if ((string = pc->read_vmcoreinfo("NUMBER(PHYS_OFFSET)"))) {
> > > > - ms->phys_offset = htol(string, QUIET, NULL);
> > > > + ms->phys_offset_nominal = htol(string, QUIET, NULL);
> > > > + if (ms->phys_offset_nominal < 0)
> > > > + ms->phys_offset = ms->phys_offset_nominal +
> > > > MEMSTART_ADDR_OFFSET;
> > > > + else
> > > > + ms->phys_offset = ms->phys_offset_nominal;
> > > > free(string);
> > > > return;
> > > > }
> > >
> > > If it's /dev/mem (not /proc/kcore), the memstart_addr value is still negative?
> > > It's no problem?
> >
> > I have no big picture about /dev/mem.
> > But for the value, memstart_addr's calculation is done by
> > arch/arm64/mm/init.c:349: memstart_addr -= _PAGE_OFFSET(48) - _PAGE_OFFSET(52);
> > in arm64_memblock_init().
> >
> > Does it raise issue for /dev/mem ? Could you enlighten me about your idea?
>
> Recently /proc/kcore has had ELF note vmcoreinfo, so crash can read it, but
> in case of /dev/mem, it cannot be used and crash will read the memstart_addr
> value with the following READMEM(). In this case, I thought that the same
> offset adjustment would be needed in theory.
>
OK, got the picture. I think you are right.
> if (ACTIVE()) {
> ...
> if ((machdep->flags & NEW_VMEMMAP) &&
> ms->kimage_voffset && (sp = kernel_symbol_search("memstart_addr"))) {
> if (pc->flags & PROC_KCORE) {
> if ((string = pc->read_vmcoreinfo("NUMBER(PHYS_OFFSET)"))) {
> ms->phys_offset_nominal = htol(string, QUIET, NULL);
> if (ms->phys_offset_nominal < 0)
> ms->phys_offset = ms->phys_offset_nominal + MEMSTART_ADDR_OFFSET;
> else
> ms->phys_offset = ms->phys_offset_nominal;
> free(string);
> return;
> }
> vaddr = symbol_value_from_proc_kallsyms("memstart_addr");
> if (vaddr == BADVAL)
> vaddr = sp->value;
> paddr = KCORE_USE_VADDR;
> } else {
> vaddr = sp->value;
> paddr = sp->value - machdep->machspec->kimage_voffset;
> }
> if (READMEM(pc->mfd, &phys_offset, sizeof(phys_offset),
> vaddr, paddr) > 0) {
> ms->phys_offset = phys_offset; <<-- read from memstart_addr
I will ditto.
> return;
> }
>
> > >
> > > > @@ -1085,7 +1106,18 @@ arm64_calc_phys_offset(void)
> > > > } else if (DISKDUMP_DUMPFILE() && diskdump_phys_base(&phys_offset)) {
> > > > ms->phys_offset = phys_offset;
> > >
> > > makedumpfile also set kdump_sub_header.phys_base to NUMBER(PHYS_OFFSET) ?
> >
> > I miss this diskdump. It should also have the same logic.
> >
> > diff --git a/arm64.c b/arm64.c
> > index 6346753..cd84a74 100644
> > --- a/arm64.c
> > +++ b/arm64.c
> > @@ -1108,9 +1108,8 @@ arm64_calc_phys_offset(void)
> > return;
> >
> > ms->phys_offset = phys_offset;
> > - } else if (DISKDUMP_DUMPFILE() && diskdump_phys_base(&phys_offset)) {
> > - ms->phys_offset = phys_offset;
> > - } else if (KDUMP_DUMPFILE() && arm64_kdump_phys_base(&phys_offset)) {
> > + } else if ((DISKDUMP_DUMPFILE() && diskdump_phys_base(&phys_offset)) ||
> > + (KDUMP_DUMPFILE() && arm64_kdump_phys_base(&phys_offset))) {
>
> Oh, this looks nicely done.
>
> > /*
> > * When running a 52bits kernel on 48bits hardware. Kernel plays a trick:
> > * if (IS_ENABLED(CONFIG_ARM64_VA_BITS_52) && (vabits_actual != 52))
> > --
> > 2.29.2
> >
> > >
> > > > } else if (KDUMP_DUMPFILE() && arm64_kdump_phys_base(&phys_offset)) {
> > > > - ms->phys_offset = phys_offset;
> > > > + /*
> > > > + * When running a 52bits kernel on 48bits hardware. Kernel plays a trick:
> > > > + * if (IS_ENABLED(CONFIG_ARM64_VA_BITS_52) && (vabits_actual != 52))
> > > > + * memstart_addr -= _PAGE_OFFSET(48) - _PAGE_OFFSET(52);
> > > > + *
> > > > + * In crash, this should be detected to get a real physical start address.
> > > > + */
> > > > + ms->phys_offset_nominal = phys_offset;
> > > > + if ((long)phys_offset < 0)
> > > > + ms->phys_offset = phys_offset + MEMSTART_ADDR_OFFSET;
> > > > + else
> > > > + ms->phys_offset = phys_offset;
> > > > } else {
> > > > error(WARNING,
> > > > "phys_offset cannot be determined from the dumpfile.\n");
> > > > @@ -1175,6 +1207,23 @@ arm64_init_kernel_pgd(void)
> > > > vt->kernel_pgd[i] = value;
> > > > }
> > > >
> > > > +ulong arm64_PTOV(ulong paddr)
> > > > +{
> > > > + ulong v;
> > > > + struct machine_specific *ms = machdep->machspec;
> > > > +
> > > > + /*
> > > > + * Either older kernel before kernel has 'physvirt_offset' or newer kernel which
> > > > + * removes 'physvirt_offset' has the same formula
> > > > + */
> > > > + if (!(machdep->flags & HAS_PHYSVIRT_OFFSET))
> > > > + v = (paddr - ms->physvirt_offset) | PAGE_OFFSET;
> > > > + else
> > > > + v = paddr - ms->physvirt_offset;
> > > > +
> > > > + return v;
> > > > +}
> > > > +
> > > > ulong
> > > > arm64_VTOP(ulong addr)
> > > > {
> > > > @@ -1185,8 +1234,20 @@ arm64_VTOP(ulong addr)
> > > > return addr - machdep->machspec->kimage_voffset;
> > > > }
> > > >
> > > > - if (addr >= machdep->machspec->page_offset)
> > > > - return addr + machdep->machspec->physvirt_offset;
I had thought it worked for all versions before commit 5383cc6efed1 (arm64: mm: Introduce vabits_actual).
So !(machdep->flags & FLIPPED_VM) branch should use the formula.
But it turns out to be wrong. PLS see the comment followed.
> > > > + if (addr >= machdep->machspec->page_offset) {
> > > > + ulong paddr;
> > > > +
> > > > + if (!(machdep->flags & FLIPPED_VM) || (machdep->flags & HAS_PHYSVIRT_OFFSET)) {
> > > > + paddr = addr;
> > > > + } else {
> > > > + /*
> > > > + * #define __lm_to_phys(addr) (((addr) & ~PAGE_OFFSET) + PHYS_OFFSET)
> > > > + */
> > > > + paddr = addr & ~ _PAGE_OFFSET(machdep->machspec->CONFIG_ARM64_VA_BITS);
> > > > + }
> > > > + paddr += machdep->machspec->physvirt_offset;
> > > > + return paddr;
> > >
> > > Hmm, complex. It should be symmetric to PTOV, why differences?
> >
[...]
>
> Yes, it's one of them, and this looks better, but...
>
> Hmm ok, I summarized these and smy question why they're asymmetric emerged:
>
Thank you for the patient.
> if physvirt_offset exists // HAS_PHYSVIRT_OFFSET
> ms->physvirt_offset = read physvirt_offset;
> else if (machdep->flags & FLIPPED_VM)
> ms->physvirt_offset = ms->phys_offset_nominal;
> else // !FLIPPED_VM
> ms->physvirt_offset = ms->phys_offset - ms->page_offset;
>
> PTOV:
> if (machdep->flags & HAS_PHYSVIRT_OFFSET)
> v = paddr - ms->physvirt_offset; // looks ok
> else
> v = (paddr - ms->physvirt_offset) | PAGE_OFFSET; // Is this ok when !FLIPPED_VM ?
>
It works for !FLIPPED_VM. But I did make a mistake on VTOP()
Flipped mm is introduced by 14c127c957c1 ("arm64: mm: Flip kernel VA space")
$ git show 14c127c957c1c6070647c171e72f06e0db275ebf:arch/arm64/include/asm/memory.h | grep "#define __phys_to_virt"
#define __phys_to_virt(x) ((unsigned long)((x) - PHYS_OFFSET) | PAGE_OFFSET)
$ git show 14c127c957c1c6070647c171e72f06e0db275ebf~1:arch/arm64/include/asm/memory.h | grep "#define __phys_to_virt"
#define __phys_to_virt(x) ((unsigned long)((x) - PHYS_OFFSET) | PAGE_OFFSET)
So the formula keeps unchange across filpped-mm. The same case for VTOP.
And what matters is physvirt_offset introduced by 5383cc6efed1 ("arm64: mm: Introduce vabits_actual")
> VTOP:
> if (machdep->flags & HAS_PHYSVIRT_OFFSET || !(machdep->flags & FLIPPED_VM))
> p = vaddr + ms->physvirt_offset; // looks ok
> else
> p = (vaddr & ~PAGE_OFFSET) + ms->physvirt_offset; // looks ok
>
Similar,
$git show 14c127c957c1c6070647c171e72f06e0db275ebf:arch/arm64/include/asm/memory.h | grep __lm_to_phys
#define __lm_to_phys(addr) (((addr) & ~PAGE_OFFSET) + PHYS_OFFSET)
__is_lm_address(__x) ? __lm_to_phys(__x) : \
$ git show 14c127c957c1c6070647c171e72f06e0db275ebf~1:arch/arm64/include/asm/memory.h | grep __lm_to_phys
#define __lm_to_phys(addr) (((addr) & ~PAGE_OFFSET) + PHYS_OFFSET)
__is_lm_address(__x) ? __lm_to_phys(__x) : \
>
> When !FLIPPED_VM, PTOV calculates:
> v = (paddr - ms->physvirt_offset) | PAGE_OFFSET
> = (paddr - ms->physoffset + ms->page_offset) | PAGE_OFFSET
>
> This might be not wrong in the result value because of the or operation,
> but looks wrong formula. So PTOV also needs the !(machdep->flags & FLIPPED_VM)
> condition? or I'm missing something?
>
So I need to drop the !(machdep->flags & FLIPPED_VM) in VTOP(), instead of adding in PTOV().
Sorry for the confusion and hope I make it clear.
Thanks,
Pingfan
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