On Wed, Dec 15, 2021 at 9:06 PM Signed-off-by@xxxxxxxxxxxx:Simon
Horman <horms@xxxxxxxxxxxx> wrote:
>
> On Fri, Dec 10, 2021 at 11:07:35AM +0800, Pingfan Liu wrote:
> > phys_to_virt() calculates virtual address. As a important factor,
> > page_offset is excepted to be accurate.
> >
> > Since arm64 kernel exposes va_bits through vmcore, using it.
> >
> > Signed-off-by: Pingfan Liu <piliu@xxxxxxxxxx>
> > ---
> > kexec/arch/arm64/kexec-arm64.c | 31 +++++++++++++++++++++++++++----
> > kexec/arch/arm64/kexec-arm64.h | 1 +
> > util_lib/elf_info.c | 5 +++++
> > 3 files changed, 33 insertions(+), 4 deletions(-)
> >
> > diff --git a/kexec/arch/arm64/kexec-arm64.c b/kexec/arch/arm64/kexec-arm64.c
> > index bd650e6..ccc92db 100644
> > --- a/kexec/arch/arm64/kexec-arm64.c
> > +++ b/kexec/arch/arm64/kexec-arm64.c
> > @@ -54,7 +54,7 @@
> > static bool try_read_phys_offset_from_kcore = false;
> >
> > /* Machine specific details. */
> > -static int va_bits;
> > +static int va_bits = -1;
> > static unsigned long page_offset;
> >
> > /* Global varables the core kexec routines expect. */
> > @@ -876,7 +876,15 @@ static inline void set_phys_offset(long v, char *set_method)
> >
> > static int get_va_bits(void)
> > {
> > - unsigned long long stext_sym_addr = get_kernel_sym("_stext");
> > + unsigned long long stext_sym_addr;
> > +
> > + /*
> > + * if already got from kcore
> > + */
> > + if (va_bits != -1)
> > + goto out;
>
> If va_bits is exposed by the kernel then it will be used.
> Else we continue here. Are there actually cases (old kernels) where
> we expect to continue. Or could we get rid of the fallback code here?
>
va_bits is exposed by kernel commit 84c57dbd3c48 ("arm64: kernel:
arch_crash_save_vmcoreinfo() should depend on CONFIG_CRASH_CORE")
And the first kernel which contains VA_BITS is v4.19.
I have no idea about the need for old kernels. Maybe just keep the
compatible code and throw a warning to remind users?
> > +
> > + stext_sym_addr = get_kernel_sym("_stext");
> >
> > if (stext_sym_addr == 0) {
> > fprintf(stderr, "Can't get the symbol of _stext.\n");
> > @@ -900,6 +908,7 @@ static int get_va_bits(void)
> > return -1;
> > }
> >
> > +out:
> > dbgprintf("va_bits : %d\n", va_bits);
> >
> > return 0;
> > @@ -917,14 +926,27 @@ int get_page_offset(unsigned long *page_offset)
> > if (ret < 0)
> > return ret;
> >
>
> I'm confused about why there is both a (va_bits - 1)
> and va_bits case here.
>
It originates from the changes of memory layout on arm64.
And mostly it is contributed by kernel commit 14c127c957c1 ("arm64:
mm: Flip kernel VA space"),
where sees the changes:
-#define PAGE_OFFSET (UL(0xffffffffffffffff) - \
(UL(1) << (VA_BITS - 1)) + 1)
+#define PAGE_OFFSET (UL(0xffffffffffffffff) - \
+ (UL(1) << VA_BITS) + 1)
Thanks,
Pingfan
_______________________________________________
kexec mailing list
kexec@xxxxxxxxxxxxxxxxxxx
http://lists.infradead.org/mailman/listinfo/kexec
