Re: [PATCH] Fix pvops Xen detection for arm machine

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On 12/16/21 3:01 PM, HAGIO KAZUHITO(萩尾 一仁) wrote:
-----Original Message-----
On 12/16/21 2:36 PM, Qi Zheng wrote:


On 12/15/21 3:42 PM, HAGIO KAZUHITO(萩尾 一仁) wrote:
Hi Qi, Xen folks,

-----Original Message-----
Since the xen_start_info on the arm/arm64 platform is static defined:

./arm/xen/enlighten.c:40:static struct start_info _xen_start_info;
./arm/xen/enlighten.c:41:struct start_info *xen_start_info =
&_xen_start_info;
./arm/xen/enlighten.c:42:EXPORT_SYMBOL(xen_start_info);

The is_pvops_xen() in commit 4badc6229c69f5cd9da7eb7bdf400a53ec6db01a
("Fix pvops Xen detection for kernels >= v4.20") always return TRUE.
Then the following error will be reported because p2m_mid_missing
and xen_p2m_addr are not defined:

     crash: cannot resolve "p2m_top"

Fix it by using xen_vcpu_id instead of xen_start_info to detect Xen
dumps.

Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
---
   kernel.c | 21 ++++++++++++++++-----
   1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/kernel.c b/kernel.c
index f4598ea..b216fbe 100644
--- a/kernel.c
+++ b/kernel.c
@@ -10745,6 +10745,9 @@ is_pvops_xen(void)
   {
       ulong addr;
       char *sym;
+    struct syment * sp;
+    ulong ptr;
+    int i;

       if (!PVOPS())
           return FALSE;
@@ -10757,11 +10760,19 @@ is_pvops_xen(void)
            STREQ(sym, "paravirt_patch_default")))
           return TRUE;

-    if (symbol_exists("xen_start_info") &&
-        readmem(symbol_value("xen_start_info"), KVADDR, &addr,
-        sizeof(void *), "xen_start_info", RETURN_ON_ERROR) &&
-        addr != 0)
-        return TRUE;
+    sp = per_cpu_symbol_search("xen_vcpu_id");
+    if (sp) {
+        for (i = 0; i < NR_CPUS; i++) {
+            if (!kt->__per_cpu_offset[i])
+                continue;

Thanks for the patch.

But seems that kt->__per_cpu_offset is initialized after the
is_pvops_xen()
call.  So this block always return FALSE?

Is there any other variable that we can use?  or another solution..

Or use xen_vcpu_info for arm/arm64 machine and xen_start_info for x86
machine? Both of these variables are assigned during the initialization
path.

Like this:

diff --git a/kernel.c b/kernel.c
index f4598ea..4b4d789 100644
--- a/kernel.c
+++ b/kernel.c
@@ -10757,11 +10757,18 @@ is_pvops_xen(void)
   	     STREQ(sym, "paravirt_patch_default")))
   		return TRUE;

-	if (symbol_exists("xen_start_info") &&
-	    readmem(symbol_value("xen_start_info"), KVADDR, &addr,
-	    sizeof(void *), "xen_start_info", RETURN_ON_ERROR) &&
-	    addr != 0)
+	if (machine_type("ARM") || machine_type("ARM64")) {
+		if (symbol_exists("xen_vcpu_info") &&
+		    readmem(symbol_value("xen_vcpu_info"), KVADDR, &addr,
+		    sizeof(void *), "xen_vcpu_info", RETURN_ON_ERROR) &&
+		    addr != 0)
+			return TRUE;
+	} else if (symbol_exists("xen_start_info") &&
+		   readmem(symbol_value("xen_start_info"), KVADDR, &addr,
+		   sizeof(void *), "xen_start_info", RETURN_ON_ERROR) &&
+		   addr != 0) {
   		return TRUE;
+	}

   	return FALSE;
   }

If it make sense, I can send the next version.

Nice, looks good to me.

I sent the patch v2. But I missed marking v2 on the subject title,
do I need to resend it?

Thanks,
Qi


Thanks,
Kazu



--
Thanks,
Qi

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