From: Takuya Yoshikawa <takuya.yoshikawa@gmail.com>
To: kvm-ia64@vger.kernel.org
Subject: [RFC][PATCH 5/12] x86: introduce __set_bit() like function for
Date: Tue, 04 May 2010 13:02:47 +0000 [thread overview]
Message-ID: <20100504220247.2e97ac01.takuya.yoshikawa@gmail.com> (raw)
During the work of KVM's dirty page logging optimization, we encountered
the need of manipulating bitmaps in user space efficiantly. To achive this,
we introduce a uaccess function for setting a bit in user space following
Avi's suggestion.
KVM is now using dirty bitmaps for live-migration and VGA. Although we need
to update them from kernel side, copying them every time for updating the
dirty log is a big bottleneck. Especially, we tested that zero-copy bitmap
manipulation improves responses of GUI manipulations a lot.
We also found one similar need in drivers/vhost/vhost.c in which the author
implemented set_bit_to_user() locally using inefficient functions: see TODO
at the top of that.
Probably, this kind of need would be common for virtualization area.
So we introduce a macro set_bit_user_non_atomic() following the implementation
style of x86's uaccess functions.
Note: there is a one restriction to this macro: bitmaps must be 64-bit
aligned (see the comment in this patch).
Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
CC: Avi Kivity <avi@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
CC: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
---
arch/x86/include/asm/uaccess.h | 39 +++++++++++++++++++++++++++++++++++++++
1 files changed, 39 insertions(+), 0 deletions(-)
diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index abd3e0e..3138e65 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -98,6 +98,45 @@ struct exception_table_entry {
extern int fixup_exception(struct pt_regs *regs);
+/**
+ * set_bit_user_non_atomic: - set a bit of a bitmap in user space.
+ * @nr: Bit offset.
+ * @addr: Base address of a bitmap in user space.
+ *
+ * Context: User context only. This function may sleep.
+ *
+ * This macro set a bit of a bitmap in user space.
+ *
+ * Restriction: the bitmap pointed to by @addr must be 64-bit aligned:
+ * the kernel accesses the bitmap by its own word length, so bitmaps
+ * allocated by 32-bit processes may cause fault.
+ *
+ * Returns zero on success, or -EFAULT on error.
+ */
+#define __set_bit_user_non_atomic_asm(nr, addr, err, errret) \
+ asm volatile("1: bts %1,%2\n" \
+ "2:\n" \
+ ".section .fixup,\"ax\"\n" \
+ "3: mov %3,%0\n" \
+ " jmp 2b\n" \
+ ".previous\n" \
+ _ASM_EXTABLE(1b, 3b) \
+ : "=r"(err) \
+ : "r" (nr), "m" (__m(addr)), "i" (errret), "0" (err))
+
+#define set_bit_user_non_atomic(nr, addr) \
+({ \
+ int __ret_sbu; \
+ \
+ might_fault(); \
+ if (access_ok(VERIFY_WRITE, addr, nr/8 + 1)) \
+ __set_bit_user_non_atomic_asm(nr, addr, __ret_sbu, -EFAULT);\
+ else \
+ __ret_sbu = -EFAULT; \
+ \
+ __ret_sbu; \
+})
+
/*
* These are the main single-value transfer routines. They automatically
* use the right size if we just have the right pointer type.
--
1.7.0.4
reply other threads:[~2010-05-04 13:02 UTC|newest]
Thread overview: [no followups] expand[flat|nested] mbox.gz Atom feed
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20100504220247.2e97ac01.takuya.yoshikawa@gmail.com \
--to=takuya.yoshikawa@gmail.com \
--cc=kvm-ia64@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).