Thank you for the update, Song.
On Mon, Aug 14, 2023 at 9:54 AM <crash-utility-request@redhat.com> wrote:
Date: Fri,  4 Aug 2023 17:15:59 +0800
From: Song Shuai <suagrfillet@gmail.com>
To: xianting.tian@linux.alibaba.com, mick@ics.forth.gr,
        heinrich.schuchardt@canonical.com, guoren@kernel.org,
        k-hagio-ab@nec.com, yixun.lan@gmail.com, lijiang@redhat.com
Cc: linux-riscv@lists.infradead.org, kexec@lists.infradead.org,
        crash-utility@redhat.com, Song Shuai <suagrfillet@gmail.com>
Subject: [Crash-utility] [Crash-utility PATCH V2] RISCV64: Use
        va_kernel_pa_offset in VTOP()
Message-ID: <20230804091559.3005820-1-suagrfillet@gmail.com>
Content-Type: text/plain; charset="US-ASCII"; x-default=true

Since RISC-V Linux v6.4, the commit 3335068f8721 ("riscv: Use
PUD/P4D/PGD pages for the linear mapping") changes phys_ram_base from
the physical start of the kernel to the actual start of the DRAM.

The Crash's VTOP() still uses phys_ram_base and kernel_map.virt_addr
to translate kernel virtual address, that made Crash boot failed with
Linux v6.4 and later version.

Let Linux export kernel_map.va_kernel_pa_offset in v6.5 and backported
v6.4.0 stable, so Crash can use "va_kernel_pa_offset" to translate the
kernel virtual address in VTOP() correctly.

Signed-off-by: Song Shuai <suagrfillet@gmail.com>
---
Changes since V1:
  - remove unnecessary first kernel version check as Kazu suggested
  - amend the commit-msg as Alex suggested
---
 defs.h    |  4 ++--
 riscv64.c | 23 +++++++++++++++++++++++
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/defs.h b/defs.h
index 5ee60f1..c07e6d7 100644
--- a/defs.h
+++ b/defs.h
@@ -3662,8 +3662,7 @@ typedef signed int s32;
        ulong _X = X;                                                                   \
        (THIS_KERNEL_VERSION >= LINUX(5,13,0) &&                                        \
                (_X) >= machdep->machspec->kernel_link_addr) ?                          \
-               (((unsigned long)(_X)-(machdep->machspec->kernel_link_addr)) +          \
-                machdep->machspec->phys_base):                                         \
+               ((unsigned long)(_X)-(machdep->machspec->va_kernel_pa_offset)):         \
                (((unsigned long)(_X)-(machdep->kvbase)) +                              \
                 machdep->machspec->phys_base);                                         \
        })
@@ -7021,6 +7020,7 @@ struct machine_specific {
        ulong modules_vaddr;
        ulong modules_end;
        ulong kernel_link_addr;
+       ulong va_kernel_pa_offset;

        ulong _page_present;
        ulong _page_read;
diff --git a/riscv64.c b/riscv64.c
index 6b9a688..7b5dd3d 100644
--- a/riscv64.c
+++ b/riscv64.c
@@ -418,6 +418,28 @@ error:
        error(FATAL, "cannot get vm layout\n");
 }

+static void
+riscv64_get_va_kernel_pa_offset(struct machine_specific *ms)
+{
+       unsigned long kernel_version = riscv64_get_kernel_version();
+
+       /*
+        * Since Linux v6.4 phys_base is not the physical start of the kernel,
+        * trying to use "va_kernel_pa_offset" to determine the offset between
+        * kernel virtual and physical addresses.
+        */
+       if (kernel_version >= LINUX(6,4,0)) {
 
Is it possible to detect the existence of the symbol 'linear_mapping_va_to_pa' or 'linear_mapping_pa_to_va' to decide reading the value of 'va_kernel_pa_offset'? For example: kernel_symbol_exists()/symbol_exists()

if (kernel_symbol_exists("linear_mapping_va_to_pa") || kernel_symbol_exists("linear_mapping_pa_to_va")) {
    string = pc->read_vmcoreinfo("NUMBER(va_kernel_pa_offset)");
    ...
}

I saw the commit 3335068f8721 exported two symbols:

+phys_addr_t linear_mapping_va_to_pa(unsigned long x)
+{
+       BUG_ON(!kernel_map.va_pa_offset);
+
+       return ((unsigned long)(x) - kernel_map.va_pa_offset);
+}
+EXPORT_SYMBOL(linear_mapping_va_to_pa);
+
+void *linear_mapping_pa_to_va(unsigned long x)
+{
+       BUG_ON(!kernel_map.va_pa_offset);
+
+       return ((void *)((unsigned long)(x) + kernel_map.va_pa_offset));
+}
+EXPORT_SYMBOL(linear_mapping_pa_to_va);

Thanks.
Lianbo

+               char *string;
+               if ((string = pc->read_vmcoreinfo("NUMBER(va_kernel_pa_offset)"))) {
+                       ms->va_kernel_pa_offset = htol(string, QUIET, NULL);
+                       free(string);
+               } else
+                       error(FATAL, "cannot read va_kernel_pa_offset\n");
+       }
+       else
+               ms->va_kernel_pa_offset = ms->kernel_link_addr - ms->phys_base;
+}
+
 static int
 riscv64_is_kvaddr(ulong vaddr)
 {
@@ -1352,6 +1374,7 @@ riscv64_init(int when)
                riscv64_get_struct_page_size(machdep->machspec);
                riscv64_get_va_bits(machdep->machspec);
                riscv64_get_va_range(machdep->machspec);
+               riscv64_get_va_kernel_pa_offset(machdep->machspec);

                pt_level_alloc(&machdep->pgd, "cannot malloc pgd space.");
                pt_level_alloc(&machdep->machspec->p4d, "cannot malloc p4d space.");
--
2.20.1