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Re: [PATCH v2 fixed 08/16] util/mmap-alloc: Factor out calculation of pa
From: |
Peter Xu |
Subject: |
Re: [PATCH v2 fixed 08/16] util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize() |
Date: |
Mon, 24 Feb 2020 12:36:28 -0500 |
On Mon, Feb 24, 2020 at 11:57:03AM +0100, David Hildenbrand wrote:
> On 24.02.20 11:50, David Hildenbrand wrote:
> > On 19.02.20 23:46, Peter Xu wrote:
> >> On Wed, Feb 12, 2020 at 02:42:46PM +0100, David Hildenbrand wrote:
> >>> Factor it out and add a comment.
> >>>
> >>> Reviewed-by: Igor Kotrasinski <address@hidden>
> >>> Acked-by: Murilo Opsfelder Araujo <address@hidden>
> >>> Reviewed-by: Richard Henderson <address@hidden>
> >>> Cc: "Michael S. Tsirkin" <address@hidden>
> >>> Cc: Murilo Opsfelder Araujo <address@hidden>
> >>> Cc: Greg Kurz <address@hidden>
> >>> Cc: Eduardo Habkost <address@hidden>
> >>> Cc: "Dr. David Alan Gilbert" <address@hidden>
> >>> Cc: Igor Mammedov <address@hidden>
> >>> Signed-off-by: David Hildenbrand <address@hidden>
> >>> ---
> >>> util/mmap-alloc.c | 21 ++++++++++++---------
> >>> 1 file changed, 12 insertions(+), 9 deletions(-)
> >>>
> >>> diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
> >>> index 27dcccd8ec..82f02a2cec 100644
> >>> --- a/util/mmap-alloc.c
> >>> +++ b/util/mmap-alloc.c
> >>> @@ -82,17 +82,27 @@ size_t qemu_mempath_getpagesize(const char *mem_path)
> >>> return qemu_real_host_page_size;
> >>> }
> >>>
> >>> +static inline size_t mmap_pagesize(int fd)
> >>> +{
> >>> +#if defined(__powerpc64__) && defined(__linux__)
> >>> + /* Mappings in the same segment must share the same page size */
> >>> + return qemu_fd_getpagesize(fd);
> >>> +#else
> >>> + return qemu_real_host_page_size;
> >>> +#endif
> >>> +}
> >>
> >> Pure question: This will return 4K even for huge pages on x86, is this
> >> what we want?
> >
> > (was asking myself the same question) I *think* it's intended. It's
> > mainly only used to allocate one additional guard page. The callers of
> > qemu_ram_mmap() make sure that the size is properly aligned (e.g., to
> > huge pages).
> >
> > Of course, a 4k guard page is sufficient - unless we can't use that
> > (special case for ppc64 here).
> >
> > Thanks!
> >
>
> We could rename the function to mmap_guard_pagesize(), thoughts?
Yeh this looks better.
Out of topic: Actually I'm still confused on why we'd need to do so
much to just leave an PROT_NONE page after the buffer. If the
hypervisor is buggy, it can logically writes to anywhere after all.
It's not a stack structure but it can be any guest RAM so I'm not sure
overflow detection really matters that much...
Thanks,
--
Peter Xu
- [PATCH v2 fixed 07/16] exec: Drop "shared" parameter from ram_block_add(), (continued)
- [PATCH v2 fixed 07/16] exec: Drop "shared" parameter from ram_block_add(), David Hildenbrand, 2020/02/12
- [PATCH v2 fixed 08/16] util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize(), David Hildenbrand, 2020/02/12
- Re: [PATCH v2 fixed 08/16] util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize(), Peter Xu, 2020/02/19
- Re: [PATCH v2 fixed 08/16] util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize(), David Hildenbrand, 2020/02/24
- Re: [PATCH v2 fixed 08/16] util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize(), David Hildenbrand, 2020/02/24
- Re: [PATCH v2 fixed 08/16] util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize(), Murilo Opsfelder Araújo, 2020/02/24
- Re: [PATCH v2 fixed 08/16] util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize(), Murilo Opsfelder Araújo, 2020/02/24
- Re: [PATCH v2 fixed 08/16] util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize(), David Hildenbrand, 2020/02/24
- Re: [PATCH v2 fixed 08/16] util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize(), David Hildenbrand, 2020/02/26
- Re: [PATCH v2 fixed 08/16] util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize(),
Peter Xu <=
- Re: [PATCH v2 fixed 08/16] util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize(), David Hildenbrand, 2020/02/24
[PATCH v2 fixed 09/16] util/mmap-alloc: Factor out reserving of a memory region to mmap_reserve(), David Hildenbrand, 2020/02/12
[PATCH v2 fixed 10/16] util/mmap-alloc: Factor out populating of memory to mmap_populate(), David Hildenbrand, 2020/02/12
[PATCH v2 fixed 11/16] util/mmap-alloc: Prepare for resizable mmaps, David Hildenbrand, 2020/02/12
[PATCH v2 fixed 12/16] util/mmap-alloc: Implement resizable mmaps, David Hildenbrand, 2020/02/12