[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH] Permit -mem-path without sync mmu
From: |
Marcelo Tosatti |
Subject: |
Re: [Qemu-devel] [PATCH] Permit -mem-path without sync mmu |
Date: |
Fri, 5 Aug 2011 12:30:53 -0300 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Fri, Aug 05, 2011 at 08:16:42AM +0200, Jan Kiszka wrote:
> On 2011-08-05 06:02, David Gibson wrote:
> > At present, an explicit test disallows use of -mem-path when kvm is enabled
> > but KVM_CAP_SYNC_MMU is not set. In particular, this prevents the user
> > from using hugetlbfs to back the guest memory.
> >
> > I can see no reason for this check, and when I asked about it previously,
> > the only theory offered was that this was a limitation of the very early
> > days of kvm which only happened to match the SYNC_MMU flag by accident.
> >
> > This patch, therefore, removes the check. This is of particular use to
> > us on POWER, where we haven't yet implement SYNC_MMU, but where backing
> > the guest with hugepages is possible, and in fact mandatory (for now).
> >
> > Signed-off-by: David Gibson <address@hidden>
> > ---
> > exec.c | 5 -----
> > 1 files changed, 0 insertions(+), 5 deletions(-)
> >
> > diff --git a/exec.c b/exec.c
> > index 476b507..041637c 100644
> > --- a/exec.c
> > +++ b/exec.c
> > @@ -2818,11 +2818,6 @@ static void *file_ram_alloc(RAMBlock *block,
> > return NULL;
> > }
> >
> > - if (kvm_enabled() && !kvm_has_sync_mmu()) {
> > - fprintf(stderr, "host lacks kvm mmu notifiers, -mem-path
> > unsupported\n");
> > - return NULL;
> > - }
> > -
> > if (asprintf(&filename, "%s/qemu_back_mem.XXXXXX", path) == -1) {
> > return NULL;
> > }
>
> This is nothing trivial, see ce9a92411d in qemu-kvm or
> http://thread.gmane.org/gmane.comp.emulators.kvm.devel/27380. And it
> should rather target uq/master. CCing Avi, Marcelo, and the kvm list.
>
> Jan
Yes, the check cannot be removed because there is the possibility of
corruption using hugepages without mmu notifiers (described in the
archived message above).
Why are mmu notifiers not implemented for PPC again?
- [Qemu-devel] [PATCH] Permit -mem-path without sync mmu, David Gibson, 2011/08/05
- Re: [Qemu-devel] [PATCH] Permit -mem-path without sync mmu, Jan Kiszka, 2011/08/05
- Re: [Qemu-devel] [PATCH] Permit -mem-path without sync mmu,
Marcelo Tosatti <=
- Re: [Qemu-devel] [PATCH] Permit -mem-path without sync mmu, David Gibson, 2011/08/08
- Re: [Qemu-devel] [PATCH] Permit -mem-path without sync mmu, Avi Kivity, 2011/08/08
- Re: [Qemu-devel] [PATCH] Permit -mem-path without sync mmu, David Gibson, 2011/08/10
- Re: [Qemu-devel] [PATCH] Permit -mem-path without sync mmu, Avi Kivity, 2011/08/10
- Re: [Qemu-devel] [PATCH] Permit -mem-path without sync mmu, David Gibson, 2011/08/11