From: Takuya Yoshikawa <takuya.yoshikawa@gmail.com>
To: Takuya Yoshikawa <takuya.yoshikawa@gmail.com>
Cc: linux-arch@vger.kernel.org, x86@kernel.org, arnd@arndb.de,
kvm@vger.kernel.org, kvm-ia64@vger.kernel.org,
fernando@oss.ntt.co.jp, mtosatti@redhat.com, agraf@suse.de,
kvm-ppc@vger.kernel.org, linux-kernel@vger.kernel.org,
yoshikawa.takuya@oss.ntt.co.jp, linuxppc-dev@ozlabs.org,
mingo@redhat.com, paulus@samba.org, avi@redhat.com,
hpa@zytor.com, tglx@linutronix.de
Subject: [RFC][PATCH 5/12] x86: introduce __set_bit() like function for bitmaps in user space
Date: Tue, 4 May 2010 22:02:47 +0900 [thread overview]
Message-ID: <20100504220247.2e97ac01.takuya.yoshikawa@gmail.com> (raw)
In-Reply-To: <20100504215645.6448af8f.takuya.yoshikawa@gmail.com>
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
next prev parent reply other threads:[~2010-05-04 13:02 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-05-04 12:56 [RFC][PATCH 0/12] KVM, x86, ppc, asm-generic: moving dirty bitmaps to user space Takuya Yoshikawa
2010-05-04 12:58 ` [RFC][PATCH 1/12 applied today] KVM: x86: avoid unnecessary bitmap allocation when memslot is clean Takuya Yoshikawa
2010-05-04 13:00 ` [RFC][PATCH 2/12] KVM: introduce slot level dirty state management Takuya Yoshikawa
2010-05-04 13:01 ` [RFC][PATCH 3/12] KVM: introduce wrapper functions to create and destroy dirty bitmaps Takuya Yoshikawa
2010-05-04 13:02 ` [RFC][PATCH 4/12] x86: introduce copy_in_user() for 32-bit Takuya Yoshikawa
2010-05-04 13:02 ` Takuya Yoshikawa [this message]
2010-05-04 13:03 ` [RFC][PATCH 6/12 not tested yet] PPC: " Takuya Yoshikawa
2010-05-04 13:04 ` [RFC][PATCH 7/12 not tested yet] PPC: introduce __set_bit() like function for bitmaps in user space Takuya Yoshikawa
2010-05-11 16:00 ` Alexander Graf
2010-05-12 9:25 ` Takuya Yoshikawa
2010-05-04 13:05 ` [RFC][PATCH resend 8/12] asm-generic: bitops: introduce le bit offset macro Takuya Yoshikawa
2010-05-04 15:03 ` Arnd Bergmann
2010-05-04 16:08 ` Avi Kivity
2010-05-05 2:59 ` Takuya Yoshikawa
2010-05-06 13:38 ` Arnd Bergmann
2010-05-10 11:46 ` Takuya Yoshikawa
2010-05-10 12:01 ` Avi Kivity
2010-05-10 12:01 ` Arnd Bergmann
2010-05-10 12:09 ` Takuya Yoshikawa
2010-05-04 13:06 ` [RFC][PATCH 9/12] KVM: introduce a wrapper function of set_bit_user_non_atomic() Takuya Yoshikawa
2010-05-04 13:07 ` [RFC][PATCH RFC 10/12] KVM: move dirty bitmaps to user space Takuya Yoshikawa
2010-05-11 3:28 ` Marcelo Tosatti
2010-05-12 6:27 ` Takuya Yoshikawa
2010-05-04 13:08 ` [RFC][PATCH 11/12] KVM: introduce new API for getting/switching dirty bitmaps Takuya Yoshikawa
2010-05-11 3:43 ` Marcelo Tosatti
2010-05-11 5:53 ` Takuya Yoshikawa
2010-05-11 14:07 ` Marcelo Tosatti
2010-05-12 6:03 ` Takuya Yoshikawa
2010-05-04 13:11 ` [RFC][PATCH 12/12 sample] qemu-kvm: use " Takuya Yoshikawa
2010-05-10 12:06 ` [RFC][PATCH 0/12] KVM, x86, ppc, asm-generic: moving dirty bitmaps to user space Avi Kivity
2010-05-10 12:26 ` Takuya Yoshikawa
2010-05-11 10:11 ` Takuya Yoshikawa
2010-05-13 11:47 ` Avi Kivity
2010-05-17 9:06 ` Takuya Yoshikawa
2010-05-11 15:55 ` Alexander Graf
2010-05-12 9:19 ` Takuya Yoshikawa
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