diff options
| author | Uros Bizjak <ubizjak@gmail.com> | 2024-04-05 10:32:53 +0200 |
|---|---|---|
| committer | Juergen Gross <jgross@suse.com> | 2024-05-17 12:14:13 +0200 |
| commit | cdf9df020130237edf8860187aca3636d679aa48 (patch) | |
| tree | 54d570852c9cdad56963dc8ed2a331d6881aa385 /arch | |
| parent | a38297e3fb012ddfa7ce0321a7e5a8daeb1872b6 (diff) | |
locking/x86/xen: Use try_cmpxchg() in xen_alloc_p2m_entry()
Use try_cmpxchg() instead of cmpxchg(*ptr, old, new) == old.
The x86 CMPXCHG instruction returns success in the ZF flag,
so this change saves a compare after CMPXCHG.
Also, try_cmpxchg() implicitly assigns old *ptr value to "old"
when CMPXCHG fails. There is no need to explicitly assign
old *ptr value to the temporary, which can simplify the
surrounding source code.
No functional change intended.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: https://lore.kernel.org/r/20240405083335.507471-1-ubizjak@gmail.com
Signed-off-by: Juergen Gross <jgross@suse.com>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/xen/p2m.c | 11 |
1 files changed, 5 insertions, 6 deletions
diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c index 9bdc3b656b2c..99918beccd80 100644 --- a/arch/x86/xen/p2m.c +++ b/arch/x86/xen/p2m.c @@ -555,7 +555,6 @@ int xen_alloc_p2m_entry(unsigned long pfn) /* Separately check the mid mfn level */ unsigned long missing_mfn; unsigned long mid_mfn_mfn; - unsigned long old_mfn; mid_mfn = alloc_p2m_page(); if (!mid_mfn) @@ -565,12 +564,12 @@ int xen_alloc_p2m_entry(unsigned long pfn) missing_mfn = virt_to_mfn(p2m_mid_missing_mfn); mid_mfn_mfn = virt_to_mfn(mid_mfn); - old_mfn = cmpxchg(top_mfn_p, missing_mfn, mid_mfn_mfn); - if (old_mfn != missing_mfn) { - free_p2m_page(mid_mfn); - mid_mfn = mfn_to_virt(old_mfn); - } else { + /* try_cmpxchg() updates missing_mfn on failure. */ + if (try_cmpxchg(top_mfn_p, &missing_mfn, mid_mfn_mfn)) { p2m_top_mfn_p[topidx] = mid_mfn; + } else { + free_p2m_page(mid_mfn); + mid_mfn = mfn_to_virt(missing_mfn); } } } else { |