Message ID | 1451549555-8359-1-git-send-email-chengang@emindsoft.com.cn |
---|---|
State | New |
Headers | show |
On 31 December 2015 at 08:12, <chengang@emindsoft.com.cn> wrote: > From: Chen Gang <chengang@emindsoft.com.cn> > > mmap() size in mmap_frag() is qemu_host_page_size, but the outside calls > page_set_flags() may be not with qemu_host_page_size. So after mmap(), > call page_set_flags() in time. > > Also let addr increasing step be TARGET_PAGE_SIZE, just like another > areas have done. > > Also remove useless variable p. Please don't do multiple things in a single patch. This patch has all of: * a fix for an unnecessary inefficiency * a coding style change with no functional effects * a bug fix Mixing them up together like this makes it harder to evaluate the bug fix, which is the important part of the change. > Signed-off-by: Chen Gang <gang.chen.5i5j@gmail.com> > --- > linux-user/mmap.c | 10 ++++++---- > 1 files changed, 6 insertions(+), 4 deletions(-) > > diff --git a/linux-user/mmap.c b/linux-user/mmap.c > index 445e8c6..7920c5e 100644 > --- a/linux-user/mmap.c > +++ b/linux-user/mmap.c > @@ -151,17 +151,19 @@ static int mmap_frag(abi_ulong real_start, > > /* get the protection of the target pages outside the mapping */ > prot1 = 0; > - for(addr = real_start; addr < real_end; addr++) { > + for (addr = real_start; addr < real_end; addr += TARGET_PAGE_SIZE) { > if (addr < start || addr >= end) > prot1 |= page_get_flags(addr); > } > > if (prot1 == 0) { > /* no page was there, so we allocate one */ > - void *p = mmap(host_start, qemu_host_page_size, prot, > - flags | MAP_ANONYMOUS, -1, 0); > - if (p == MAP_FAILED) > + if (mmap(host_start, qemu_host_page_size, prot, flags | MAP_ANONYMOUS, > + -1, 0) == MAP_FAILED) { > return -1; > + } > + page_set_flags(real_start, real_start + qemu_host_page_size, > + prot | PAGE_VALID); I'm not convinced this is right -- it will mean that we set the page flags for every target page in this host page to be the same thing (the ORed together result we calculated). I don't think we want to update the page flags like that -- if one target page was read-only and the other read-write then we need to make the whole host page read-write (since it's bigger and covers both target pages), but we don't want to incorrectly record that the first target-page is read-write. I don't really understand this mmap code, though -- that's just the result of looking at it for fifteen minutes or so. > prot1 = prot; > } > prot1 &= PAGE_BITS; > -- > 1.7.3.4 > thanks -- PMM
On 2016年01月08日 03:35, Peter Maydell wrote: > > Please don't do multiple things in a single patch. This patch > has all of: > * a fix for an unnecessary inefficiency > * a coding style change with no functional effects > * a bug fix > > Mixing them up together like this makes it harder to evaluate > the bug fix, which is the important part of the change. > OK, thanks. >> diff --git a/linux-user/mmap.c b/linux-user/mmap.c >> index 445e8c6..7920c5e 100644 >> --- a/linux-user/mmap.c >> +++ b/linux-user/mmap.c >> @@ -151,17 +151,19 @@ static int mmap_frag(abi_ulong real_start, >> >> /* get the protection of the target pages outside the mapping */ >> prot1 = 0; >> - for(addr = real_start; addr < real_end; addr++) { >> + for (addr = real_start; addr < real_end; addr += TARGET_PAGE_SIZE) { >> if (addr < start || addr >= end) >> prot1 |= page_get_flags(addr); >> } >> >> if (prot1 == 0) { >> /* no page was there, so we allocate one */ >> - void *p = mmap(host_start, qemu_host_page_size, prot, >> - flags | MAP_ANONYMOUS, -1, 0); >> - if (p == MAP_FAILED) >> + if (mmap(host_start, qemu_host_page_size, prot, flags | MAP_ANONYMOUS, >> + -1, 0) == MAP_FAILED) { >> return -1; >> + } >> + page_set_flags(real_start, real_start + qemu_host_page_size, >> + prot | PAGE_VALID); > > I'm not convinced this is right -- it will mean that we set > the page flags for every target page in this host page to > be the same thing (the ORed together result we calculated). > I don't think we want to update the page flags like that -- > if one target page was read-only and the other read-write then > we need to make the whole host page read-write (since it's > bigger and covers both target pages), but we don't want to > incorrectly record that the first target-page is read-write. > OK, thanks. It looks this patch is not quite precise. I guess, we need use PAGE_VALID instead of "prot | PAGE_VALID" for page_set_flags() after mmap() in mmap_frag(). So when the next call for the same location, prot1 will be PAGE_VALID ( now, it may be 0), then can protect to enter "if (prot1 == 0)", again. > I don't really understand this mmap code, though -- that's just > the result of looking at it for fifteen minutes or so. > OK, I can understand. Thanks.
diff --git a/linux-user/mmap.c b/linux-user/mmap.c index 445e8c6..7920c5e 100644 --- a/linux-user/mmap.c +++ b/linux-user/mmap.c @@ -151,17 +151,19 @@ static int mmap_frag(abi_ulong real_start, /* get the protection of the target pages outside the mapping */ prot1 = 0; - for(addr = real_start; addr < real_end; addr++) { + for (addr = real_start; addr < real_end; addr += TARGET_PAGE_SIZE) { if (addr < start || addr >= end) prot1 |= page_get_flags(addr); } if (prot1 == 0) { /* no page was there, so we allocate one */ - void *p = mmap(host_start, qemu_host_page_size, prot, - flags | MAP_ANONYMOUS, -1, 0); - if (p == MAP_FAILED) + if (mmap(host_start, qemu_host_page_size, prot, flags | MAP_ANONYMOUS, + -1, 0) == MAP_FAILED) { return -1; + } + page_set_flags(real_start, real_start + qemu_host_page_size, + prot | PAGE_VALID); prot1 = prot; } prot1 &= PAGE_BITS;