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Re: [Qemu-devel] Re: [Qemu-commits] [COMMIT 3086844] Instead of writing

From: Avi Kivity
Subject: Re: [Qemu-devel] Re: [Qemu-commits] [COMMIT 3086844] Instead of writing a zero page, madvise it away
Date: Mon, 22 Jun 2009 21:04:34 +0300
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1b3pre) Gecko/20090513 Fedora/3.0-2.3.beta2.fc11 Thunderbird/3.0b2

On 06/22/2009 08:44 PM, Anthony Liguori wrote:
See attached.
Author: Anthony Liguori<address@hidden>
Date:   Mon Jun 22 12:39:00 2009 -0500

     Make sure to zero out memory before calling madvise to increase robustness

     Avi pointed out that it's not entirely safe to rely on madvise zeroing out
     memory.  So let's do it explicitly before calling madvise.

     Signed-off-by: Anthony Liguori<address@hidden>

diff --git a/vl.c b/vl.c
index 60a00e1..1c077b4 100644
--- a/vl.c
+++ b/vl.c
@@ -3358,13 +3358,13 @@ static int ram_load(QEMUFile *f, void *opaque, int 

          if (flags&  RAM_SAVE_FLAG_COMPRESS) {
              uint8_t ch = qemu_get_byte(f);
-#if defined(__linux__)
+            memset(qemu_get_ram_ptr(addr), ch, TARGET_PAGE_SIZE);
+#ifndef _WIN32
              if (ch == 0&&
                  (!kvm_enabled() || kvm_has_sync_mmu())) {
                  madvise(qemu_get_ram_ptr(addr), TARGET_PAGE_SIZE, 
-            } else
+            }
-            memset(qemu_get_ram_ptr(addr), ch, TARGET_PAGE_SIZE);
          } else if (flags&  RAM_SAVE_FLAG_PAGE)
              qemu_get_buffer(f, qemu_get_ram_ptr(addr), TARGET_PAGE_SIZE);
      } while (!(flags&  RAM_SAVE_FLAG_EOS));

Pretty similar to my December patch... which had another case, is it missing?


I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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