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From: Jan Beulich <jbeulich@suse.com>
To: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
	George Dunlap <george.dunlap@citrix.com>
Subject: [PATCH v2 6/8] kexec: avoid effectively open-coding xzalloc_flex_struct()
Date: Wed, 21 Apr 2021 16:58:48 +0200	[thread overview]
Message-ID: <7d6c30d8-c121-11f5-4ac9-49bad43a2a19@suse.com> (raw)
In-Reply-To: <091b4b91-712f-3526-78d1-80d31faf8e41@suse.com>

There is a difference in generated code: xzalloc_bytes() forces
SMP_CACHE_BYTES alignment. But if code really cared about such higher
than default alignment, it should request so explicitly rather than
using a type-unsafe interface. And if e.g. cache line sharing was a
concern, the allocator itself should arrange to avoid such.

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/common/kexec.c
+++ b/xen/common/kexec.c
@@ -463,7 +463,10 @@ static void * alloc_from_crash_heap(cons
 /* Allocate a crash note buffer for a newly onlined cpu. */
 static int kexec_init_cpu_notes(const unsigned long cpu)
 {
-    Elf_Note * note = NULL;
+    struct elf_notes {
+        Elf_Note first;
+        unsigned char more[];
+    } *notes = NULL;
     int ret = 0;
     int nr_bytes = 0;
 
@@ -477,7 +480,8 @@ static int kexec_init_cpu_notes(const un
 
     /* If we dont care about the position of allocation, malloc. */
     if ( low_crashinfo_mode == LOW_CRASHINFO_NONE )
-        note = xzalloc_bytes(nr_bytes);
+        notes = xzalloc_flex_struct(struct elf_notes, more,
+                                    nr_bytes - sizeof(notes->first));
 
     /* Protect the write into crash_notes[] with a spinlock, as this function
      * is on a hotplug path and a hypercall path. */
@@ -490,26 +494,28 @@ static int kexec_init_cpu_notes(const un
         spin_unlock(&crash_notes_lock);
         /* Always return ok, because whether we successfully allocated or not,
          * another CPU has successfully allocated. */
-        xfree(note);
+        xfree(notes);
     }
     else
     {
         /* If we care about memory possition, alloc from the crash heap,
          * also protected by the crash_notes_lock. */
         if ( low_crashinfo_mode > LOW_CRASHINFO_NONE )
-            note = alloc_from_crash_heap(nr_bytes);
+            notes = alloc_from_crash_heap(nr_bytes);
 
-        crash_notes[cpu].start = note;
+        crash_notes[cpu].start = &notes->first;
         crash_notes[cpu].size = nr_bytes;
         spin_unlock(&crash_notes_lock);
 
         /* If the allocation failed, and another CPU did not beat us, give
          * up with ENOMEM. */
-        if ( ! note )
+        if ( ! notes )
             ret = -ENOMEM;
         /* else all is good so lets set up the notes. */
         else
         {
+            Elf_Note *note = &notes->first;
+
             /* Set up CORE note. */
             setup_note(note, "CORE", NT_PRSTATUS, sizeof(ELF_Prstatus));
             note = ELFNOTE_NEXT(note);



  parent reply	other threads:[~2021-04-21 14:59 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-21 14:54 [PATCH v2 0/8] assorted replacement of x[mz]alloc_bytes() Jan Beulich
2021-04-21 14:56 ` [PATCH v2 1/8] x86/MCE: avoid effectively open-coding xmalloc_array() Jan Beulich
2021-04-21 14:56 ` [PATCH v2 2/8] x86/HVM: " Jan Beulich
2021-04-21 14:57 ` [PATCH v2 3/8] x86/oprofile: " Jan Beulich
2021-04-21 14:57 ` [PATCH v2 4/8] x86/IRQ: avoid over-alignment in alloc_pirq_struct() Jan Beulich
2021-04-21 14:58 ` [PATCH v2 5/8] EFI/runtime: avoid effectively open-coding x{m,z}alloc_array() Jan Beulich
2021-04-21 14:58 ` Jan Beulich [this message]
2021-04-21 14:59 ` [PATCH v2 7/8] video/lfb: avoid effectively open-coding xzalloc_array() Jan Beulich
2021-04-21 14:59 ` [PATCH v2 8/8] Arm/optee: don't open-code xzalloc_flex_struct() Jan Beulich
2021-05-03 13:53   ` Ping: " Jan Beulich
2021-05-04 23:49     ` Volodymyr Babchuk
2021-04-21 15:23 ` [PATCH v2 0/8] assorted replacement of x[mz]alloc_bytes() Andrew Cooper
2021-04-21 15:32   ` Jan Beulich
2021-04-23  9:44   ` Jan Beulich

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