Re: [Xen-devel] [PATCH] x86/xen: Remove use of VLAs

[Laura Abbott <labbott@xxxxxxxxxx>]

On 04/17/2018 12:16 AM, Juergen Gross wrote:
> On 16/04/18 15:27, Boris Ostrovsky wrote:
> > On 04/13/2018 06:11 PM, Laura Abbott wrote:
> > > There's an ongoing effort to remove VLAs[1] from the kernel to eventually
> > > turn on -Wvla. The few VLAs in use have an upper bound based on a size
> > > of 64K. This doesn't produce an excessively large stack so just switch
> > > the upper bound.
> > >
> > > [1] https://lkml.org/lkml/2018/3/7/621
> > >
> > > Signed-off-by: Laura Abbott <labbott@xxxxxxxxxx>
> > > ---
> > >   arch/x86/xen/enlighten_pv.c | 6 ++----
> > >   1 file changed, 2 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
> > > index c36d23aa6c35..d96a5a535cbb 100644
> > > --- a/arch/x86/xen/enlighten_pv.c
> > > +++ b/arch/x86/xen/enlighten_pv.c
> > > @@ -421,8 +421,7 @@ static void xen_load_gdt(const struct desc_ptr *dtr)
> > >   {
> > >         unsigned long va = dtr->address;
> > >         unsigned int size = dtr->size + 1;
> > > -       unsigned pages = DIV_ROUND_UP(size, PAGE_SIZE);
> >
> >
> > Isn't dtr->size always either GDT_SIZE or 0?
> GDT_SIZE - 1 :-)
>
> > > -       unsigned long frames[pages];
> > > +       unsigned long frames[DIV_ROUND_UP(SZ_64K, PAGE_SIZE)];
> So we could just go with one frame and modify the BUG_ON() further below
> accordingly.
Do you want to just remove the loop as well since we're never going
to do more than one frame? We end up with net code deletion.

Thanks,
Laura

> Juergen

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