[Xen-devel] Re: [GIT PULL] Xen bugfixes

[Ingo Molnar <mingo@xxxxxxx>]

* Jeremy Fitzhardinge <jeremy@xxxxxxxx> wrote:

> Hi,
> 
> Here's 3 patches which fix two Xen PV spinlock bugs, and makes 
> CONFIG_CC_STACKPROTECTOR work on both 32- and 64-bit.
> 
> The spinlock bugs are both rare races:
>  - lock can briefly hold the lock while interrupts are enabled, allowing an 
> ISR to deadlock
>  - unlock doesn't enforce CPU memory ordering between the actual unlock write 
> and the check
>    to see if there are any pending waiters, so it can end up deciding there's 
> nobody to
>    kick on unlock, leaving another CPU hanging.  It needs a full mb() to 
> guarantee the correct
>    ordering.
> 
> The stack-protector fix bites the bullet and does a full GDT setup 
> early so that we can load %gs for the stack-protector canary 
> segment on i386.  This also removes the assumption that the 
> initial percpu %fs segment has a zero base.
> 
> x86-64 still just needs the GS_BASE MSR written, but that now 
> happens using the same code as i386 rather than being special 
> cased.
> 
> Thanks,
>       J
> 
> The following changes since commit e07cccf4046978df10f2e13fe2b99b2f9b3a65db:
>   Linus Torvalds (1):
>         Linux 2.6.31-rc9
> 
> are available in the git repository at:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/jeremy/xen.git bugfix
> 
> Jeremy Fitzhardinge (2):
>       xen: make -fstack-protector work under Xen
>       xen: only enable interrupts while actually blocking for spinlock
> 
> Yang Xiaowei (1):
>       xen: use stronger barrier after unlocking lock
> 
>  arch/x86/mm/Makefile     |    4 ++
>  arch/x86/xen/Makefile    |    2 +
>  arch/x86/xen/enlighten.c |  131 
> +++++++++++++++++++++++++++++++++++++++-------
>  arch/x86/xen/smp.c       |    1 +
>  arch/x86/xen/spinlock.c  |   28 ++++++----
>  drivers/xen/Makefile     |    3 +
>  6 files changed, 140 insertions(+), 29 deletions(-)

Pulled, thanks a lot Jeremy!

A few comments:

> +# Make sure __phys_addr has no stackprotector
> +nostackp := $(call cc-option, -fno-stack-protector)
> +CFLAGS_ioremap.o             := $(nostackp)
> +

Sure we could move __phys_addr into its own file and thus avoid 
turning off stackprotector for the rest of ioremap.c?

> --- a/arch/x86/xen/Makefile
> +++ b/arch/x86/xen/Makefile
> @@ -8,6 +8,7 @@ endif
>  # Make sure early boot has no stackprotector
>  nostackp := $(call cc-option, -fno-stack-protector)
>  CFLAGS_enlighten.o           := $(nostackp)
> +CFLAGS_mmu.o                 := $(nostackp)

A similar argument could be made here - what proportion of mmu.c is 
affected?

Also, once the commits have hit upstream feel free bounce them to 
stable@xxxxxxxxxx - they dont have Cc: <stable@xxxxxxxxxx> tags for 
automatic back-merging requests. The fixes narrowly missed v2.6.31.

        Ingo

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