| Message ID | 0e5ff7f7-855c-ea28-fdee-73c062c3d289@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, Mar 15, 2017 at 01:28:07PM +0000, Marc Zyngier wrote: > On 15/03/17 10:56, Christoffer Dall wrote: > > On Wed, Mar 15, 2017 at 09:39:26AM +0000, Marc Zyngier wrote: > >> On 15/03/17 09:21, Christoffer Dall wrote: > >>> On Tue, Mar 14, 2017 at 02:52:34PM +0000, Suzuki K Poulose wrote: > >>>> In kvm_free_stage2_pgd() we don't hold the kvm->mmu_lock while calling > >>>> unmap_stage2_range() on the entire memory range for the guest. This could > >>>> cause problems with other callers (e.g, munmap on a memslot) trying to > >>>> unmap a range. > >>>> > >>>> Fixes: commit d5d8184d35c9 ("KVM: ARM: Memory virtualization setup") > >>>> Cc: stable@vger.kernel.org # v3.10+ > >>>> Cc: Marc Zyngier <marc.zyngier@arm.com> > >>>> Cc: Christoffer Dall <christoffer.dall@linaro.org> > >>>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> > >>>> --- > >>>> arch/arm/kvm/mmu.c | 3 +++ > >>>> 1 file changed, 3 insertions(+) > >>>> > >>>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c > >>>> index 13b9c1f..b361f71 100644 > >>>> --- a/arch/arm/kvm/mmu.c > >>>> +++ b/arch/arm/kvm/mmu.c > >>>> @@ -831,7 +831,10 @@ void kvm_free_stage2_pgd(struct kvm *kvm) > >>>> if (kvm->arch.pgd == NULL) > >>>> return; > >>>> > >>>> + spin_lock(&kvm->mmu_lock); > >>>> unmap_stage2_range(kvm, 0, KVM_PHYS_SIZE); > >>>> + spin_unlock(&kvm->mmu_lock); > >>>> + > >>> > >>> This ends up holding the spin lock for potentially quite a while, where > >>> we can do things like __flush_dcache_area(), which I think can fault. > >> > >> I believe we're always using the linear mapping (or kmap on 32bit) in > >> order not to fault. > >> > > > > ok, then there's just the concern that we may be holding a spinlock for > > a very long time. I seem to recall Mario once added something where he > > unlocked and gave a chance to schedule something else for each PUD or > > something like that, because he ran into the issue during migration. Am > > I confusing this with something else? > > That definitely rings a bell: stage2_wp_range() uses that kind of trick > to give the system a chance to breathe. Maybe we could use a similar > trick in our S2 unmapping code? How about this (completely untested) patch: > > diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c > index 962616fd4ddd..1786c24212d4 100644 > --- a/arch/arm/kvm/mmu.c > +++ b/arch/arm/kvm/mmu.c > @@ -292,8 +292,13 @@ static void unmap_stage2_range(struct kvm *kvm, phys_addr_t start, u64 size) > phys_addr_t addr = start, end = start + size; > phys_addr_t next; > > + BUG_ON(!spin_is_locked(&kvm->mmu_lock)); > + > pgd = kvm->arch.pgd + stage2_pgd_index(addr); > do { > + if (need_resched() || spin_needbreak(&kvm->mmu_lock)) > + cond_resched_lock(&kvm->mmu_lock); > + > next = stage2_pgd_addr_end(addr, end); > if (!stage2_pgd_none(*pgd)) > unmap_stage2_puds(kvm, pgd, addr, next); > > The additional BUG_ON() is just for my own peace of mind - we seem to > have missed a couple of these lately, and the "breathing" code makes > it imperative that this lock is being taken prior to entering the > function. > Looks good to me! -Christoffer
On 15/03/17 13:35, Christoffer Dall wrote: > On Wed, Mar 15, 2017 at 01:28:07PM +0000, Marc Zyngier wrote: >> On 15/03/17 10:56, Christoffer Dall wrote: >>> On Wed, Mar 15, 2017 at 09:39:26AM +0000, Marc Zyngier wrote: >>>> On 15/03/17 09:21, Christoffer Dall wrote: >>>>> On Tue, Mar 14, 2017 at 02:52:34PM +0000, Suzuki K Poulose wrote: >>>>>> In kvm_free_stage2_pgd() we don't hold the kvm->mmu_lock while calling >>>>>> unmap_stage2_range() on the entire memory range for the guest. This could >>>>>> cause problems with other callers (e.g, munmap on a memslot) trying to >>>>>> unmap a range. >>>>>> >>>>>> Fixes: commit d5d8184d35c9 ("KVM: ARM: Memory virtualization setup") >>>>>> Cc: stable@vger.kernel.org # v3.10+ >>>>>> Cc: Marc Zyngier <marc.zyngier@arm.com> >>>>>> Cc: Christoffer Dall <christoffer.dall@linaro.org> >>>>>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> >>>>>> --- >>>>>> arch/arm/kvm/mmu.c | 3 +++ >>>>>> 1 file changed, 3 insertions(+) >>>>>> >>>>>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c >>>>>> index 13b9c1f..b361f71 100644 >>>>>> --- a/arch/arm/kvm/mmu.c >>>>>> +++ b/arch/arm/kvm/mmu.c >>>>>> @@ -831,7 +831,10 @@ void kvm_free_stage2_pgd(struct kvm *kvm) >>>>>> if (kvm->arch.pgd == NULL) >>>>>> return; >>>>>> >>>>>> + spin_lock(&kvm->mmu_lock); >>>>>> unmap_stage2_range(kvm, 0, KVM_PHYS_SIZE); >>>>>> + spin_unlock(&kvm->mmu_lock); >>>>>> + >>>>> >>>>> This ends up holding the spin lock for potentially quite a while, where >>>>> we can do things like __flush_dcache_area(), which I think can fault. >>>> >>>> I believe we're always using the linear mapping (or kmap on 32bit) in >>>> order not to fault. >>>> >>> >>> ok, then there's just the concern that we may be holding a spinlock for >>> a very long time. I seem to recall Mario once added something where he >>> unlocked and gave a chance to schedule something else for each PUD or >>> something like that, because he ran into the issue during migration. Am >>> I confusing this with something else? >> >> That definitely rings a bell: stage2_wp_range() uses that kind of trick >> to give the system a chance to breathe. Maybe we could use a similar >> trick in our S2 unmapping code? How about this (completely untested) patch: >> >> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c >> index 962616fd4ddd..1786c24212d4 100644 >> --- a/arch/arm/kvm/mmu.c >> +++ b/arch/arm/kvm/mmu.c >> @@ -292,8 +292,13 @@ static void unmap_stage2_range(struct kvm *kvm, phys_addr_t start, u64 size) >> phys_addr_t addr = start, end = start + size; >> phys_addr_t next; >> >> + BUG_ON(!spin_is_locked(&kvm->mmu_lock)); >> + >> pgd = kvm->arch.pgd + stage2_pgd_index(addr); >> do { >> + if (need_resched() || spin_needbreak(&kvm->mmu_lock)) >> + cond_resched_lock(&kvm->mmu_lock); >> + >> next = stage2_pgd_addr_end(addr, end); >> if (!stage2_pgd_none(*pgd)) >> unmap_stage2_puds(kvm, pgd, addr, next); >> >> The additional BUG_ON() is just for my own peace of mind - we seem to >> have missed a couple of these lately, and the "breathing" code makes >> it imperative that this lock is being taken prior to entering the >> function. >> > > Looks good to me! OK. I'll stash that on top of Suzuki's series, and start running some actual tests... ;-) Thanks, M.
Hi Marc, On 15/03/17 13:43, Marc Zyngier wrote: > On 15/03/17 13:35, Christoffer Dall wrote: >> On Wed, Mar 15, 2017 at 01:28:07PM +0000, Marc Zyngier wrote: >>> On 15/03/17 10:56, Christoffer Dall wrote: >>>> On Wed, Mar 15, 2017 at 09:39:26AM +0000, Marc Zyngier wrote: >>>>> On 15/03/17 09:21, Christoffer Dall wrote: >>>>>> On Tue, Mar 14, 2017 at 02:52:34PM +0000, Suzuki K Poulose wrote: >>>>>>> In kvm_free_stage2_pgd() we don't hold the kvm->mmu_lock while calling >>>>>>> unmap_stage2_range() on the entire memory range for the guest. This could >>>>>>> cause problems with other callers (e.g, munmap on a memslot) trying to >>>>>>> unmap a range. >>>>>>> >>>>>>> Fixes: commit d5d8184d35c9 ("KVM: ARM: Memory virtualization setup") >>>>>>> Cc: stable@vger.kernel.org # v3.10+ >>>>>>> Cc: Marc Zyngier <marc.zyngier@arm.com> >>>>>>> Cc: Christoffer Dall <christoffer.dall@linaro.org> >>>>>>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> >>>>>>> --- >>>>>>> arch/arm/kvm/mmu.c | 3 +++ >>>>>>> 1 file changed, 3 insertions(+) >>>>>>> >>>>>>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c >>>>>>> index 13b9c1f..b361f71 100644 >>>>>>> --- a/arch/arm/kvm/mmu.c >>>>>>> +++ b/arch/arm/kvm/mmu.c >>>>>>> @@ -831,7 +831,10 @@ void kvm_free_stage2_pgd(struct kvm *kvm) >>>>>>> if (kvm->arch.pgd == NULL) >>>>>>> return; >>>>>>> >>>>>>> + spin_lock(&kvm->mmu_lock); >>>>>>> unmap_stage2_range(kvm, 0, KVM_PHYS_SIZE); >>>>>>> + spin_unlock(&kvm->mmu_lock); >>>>>>> + >>>>>> >>>>>> This ends up holding the spin lock for potentially quite a while, where >>>>>> we can do things like __flush_dcache_area(), which I think can fault. >>>>> >>>>> I believe we're always using the linear mapping (or kmap on 32bit) in >>>>> order not to fault. >>>>> >>>> >>>> ok, then there's just the concern that we may be holding a spinlock for >>>> a very long time. I seem to recall Mario once added something where he >>>> unlocked and gave a chance to schedule something else for each PUD or >>>> something like that, because he ran into the issue during migration. Am >>>> I confusing this with something else? >>> >>> That definitely rings a bell: stage2_wp_range() uses that kind of trick >>> to give the system a chance to breathe. Maybe we could use a similar >>> trick in our S2 unmapping code? How about this (completely untested) patch: >>> >>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c >>> index 962616fd4ddd..1786c24212d4 100644 >>> --- a/arch/arm/kvm/mmu.c >>> +++ b/arch/arm/kvm/mmu.c >>> @@ -292,8 +292,13 @@ static void unmap_stage2_range(struct kvm *kvm, phys_addr_t start, u64 size) >>> phys_addr_t addr = start, end = start + size; >>> phys_addr_t next; >>> >>> + BUG_ON(!spin_is_locked(&kvm->mmu_lock)); Nit: assert_spin_locked() is somewhat more pleasant (and currently looks to expand to the exact same code). Robin. >>> + >>> pgd = kvm->arch.pgd + stage2_pgd_index(addr); >>> do { >>> + if (need_resched() || spin_needbreak(&kvm->mmu_lock)) >>> + cond_resched_lock(&kvm->mmu_lock); >>> + >>> next = stage2_pgd_addr_end(addr, end); >>> if (!stage2_pgd_none(*pgd)) >>> unmap_stage2_puds(kvm, pgd, addr, next); >>> >>> The additional BUG_ON() is just for my own peace of mind - we seem to >>> have missed a couple of these lately, and the "breathing" code makes >>> it imperative that this lock is being taken prior to entering the >>> function. >>> >> >> Looks good to me! > > OK. I'll stash that on top of Suzuki's series, and start running some > actual tests... ;-) > > Thanks, > > M. >
On 15/03/17 13:50, Robin Murphy wrote: > Hi Marc, > > On 15/03/17 13:43, Marc Zyngier wrote: >> On 15/03/17 13:35, Christoffer Dall wrote: >>> On Wed, Mar 15, 2017 at 01:28:07PM +0000, Marc Zyngier wrote: >>>> On 15/03/17 10:56, Christoffer Dall wrote: >>>>> On Wed, Mar 15, 2017 at 09:39:26AM +0000, Marc Zyngier wrote: >>>>>> On 15/03/17 09:21, Christoffer Dall wrote: >>>>>>> On Tue, Mar 14, 2017 at 02:52:34PM +0000, Suzuki K Poulose wrote: >>>>>>>> In kvm_free_stage2_pgd() we don't hold the kvm->mmu_lock while calling >>>>>>>> unmap_stage2_range() on the entire memory range for the guest. This could >>>>>>>> cause problems with other callers (e.g, munmap on a memslot) trying to >>>>>>>> unmap a range. >>>>>>>> >>>>>>>> Fixes: commit d5d8184d35c9 ("KVM: ARM: Memory virtualization setup") >>>>>>>> Cc: stable@vger.kernel.org # v3.10+ >>>>>>>> Cc: Marc Zyngier <marc.zyngier@arm.com> >>>>>>>> Cc: Christoffer Dall <christoffer.dall@linaro.org> >>>>>>>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> >>>>>>>> --- >>>>>>>> arch/arm/kvm/mmu.c | 3 +++ >>>>>>>> 1 file changed, 3 insertions(+) >>>>>>>> >>>>>>>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c >>>>>>>> index 13b9c1f..b361f71 100644 >>>>>>>> --- a/arch/arm/kvm/mmu.c >>>>>>>> +++ b/arch/arm/kvm/mmu.c >>>>>>>> @@ -831,7 +831,10 @@ void kvm_free_stage2_pgd(struct kvm *kvm) >>>>>>>> if (kvm->arch.pgd == NULL) >>>>>>>> return; >>>>>>>> >>>>>>>> + spin_lock(&kvm->mmu_lock); >>>>>>>> unmap_stage2_range(kvm, 0, KVM_PHYS_SIZE); >>>>>>>> + spin_unlock(&kvm->mmu_lock); >>>>>>>> + >>>>>>> >>>>>>> This ends up holding the spin lock for potentially quite a while, where >>>>>>> we can do things like __flush_dcache_area(), which I think can fault. >>>>>> >>>>>> I believe we're always using the linear mapping (or kmap on 32bit) in >>>>>> order not to fault. >>>>>> >>>>> >>>>> ok, then there's just the concern that we may be holding a spinlock for >>>>> a very long time. I seem to recall Mario once added something where he >>>>> unlocked and gave a chance to schedule something else for each PUD or >>>>> something like that, because he ran into the issue during migration. Am >>>>> I confusing this with something else? >>>> >>>> That definitely rings a bell: stage2_wp_range() uses that kind of trick >>>> to give the system a chance to breathe. Maybe we could use a similar >>>> trick in our S2 unmapping code? How about this (completely untested) patch: >>>> >>>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c >>>> index 962616fd4ddd..1786c24212d4 100644 >>>> --- a/arch/arm/kvm/mmu.c >>>> +++ b/arch/arm/kvm/mmu.c >>>> @@ -292,8 +292,13 @@ static void unmap_stage2_range(struct kvm *kvm, phys_addr_t start, u64 size) >>>> phys_addr_t addr = start, end = start + size; >>>> phys_addr_t next; >>>> >>>> + BUG_ON(!spin_is_locked(&kvm->mmu_lock)); > > Nit: assert_spin_locked() is somewhat more pleasant (and currently looks > to expand to the exact same code). Fancy! Thanks, M.
On 15/03/17 13:28, Marc Zyngier wrote: > On 15/03/17 10:56, Christoffer Dall wrote: >> On Wed, Mar 15, 2017 at 09:39:26AM +0000, Marc Zyngier wrote: >>> On 15/03/17 09:21, Christoffer Dall wrote: >>>> On Tue, Mar 14, 2017 at 02:52:34PM +0000, Suzuki K Poulose wrote: >>>>> In kvm_free_stage2_pgd() we don't hold the kvm->mmu_lock while calling >>>>> unmap_stage2_range() on the entire memory range for the guest. This could >>>>> cause problems with other callers (e.g, munmap on a memslot) trying to >>>>> unmap a range. >>>>> >>>>> Fixes: commit d5d8184d35c9 ("KVM: ARM: Memory virtualization setup") >>>>> Cc: stable@vger.kernel.org # v3.10+ >>>>> Cc: Marc Zyngier <marc.zyngier@arm.com> >>>>> Cc: Christoffer Dall <christoffer.dall@linaro.org> >>>>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> ... >> ok, then there's just the concern that we may be holding a spinlock for >> a very long time. I seem to recall Mario once added something where he >> unlocked and gave a chance to schedule something else for each PUD or >> something like that, because he ran into the issue during migration. Am >> I confusing this with something else? > > That definitely rings a bell: stage2_wp_range() uses that kind of trick > to give the system a chance to breathe. Maybe we could use a similar > trick in our S2 unmapping code? How about this (completely untested) patch: > > diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c > index 962616fd4ddd..1786c24212d4 100644 > --- a/arch/arm/kvm/mmu.c > +++ b/arch/arm/kvm/mmu.c > @@ -292,8 +292,13 @@ static void unmap_stage2_range(struct kvm *kvm, phys_addr_t start, u64 size) > phys_addr_t addr = start, end = start + size; > phys_addr_t next; > > + BUG_ON(!spin_is_locked(&kvm->mmu_lock)); > + > pgd = kvm->arch.pgd + stage2_pgd_index(addr); > do { > + if (need_resched() || spin_needbreak(&kvm->mmu_lock)) > + cond_resched_lock(&kvm->mmu_lock); nit: I think we could make the cond_resched_lock() unconditionally here: Given, __cond_resched_lock() already does all the above checks : kernel/sched/core.c: int __cond_resched_lock(spinlock_t *lock) { int resched = should_resched(PREEMPT_LOCK_OFFSET); ... if (spin_needbreak(lock) || resched) { Suzuki
On 15/03/17 14:33, Suzuki K Poulose wrote: > On 15/03/17 13:28, Marc Zyngier wrote: >> On 15/03/17 10:56, Christoffer Dall wrote: >>> On Wed, Mar 15, 2017 at 09:39:26AM +0000, Marc Zyngier wrote: >>>> On 15/03/17 09:21, Christoffer Dall wrote: >>>>> On Tue, Mar 14, 2017 at 02:52:34PM +0000, Suzuki K Poulose wrote: >>>>>> In kvm_free_stage2_pgd() we don't hold the kvm->mmu_lock while calling >>>>>> unmap_stage2_range() on the entire memory range for the guest. This could >>>>>> cause problems with other callers (e.g, munmap on a memslot) trying to >>>>>> unmap a range. >>>>>> >>>>>> Fixes: commit d5d8184d35c9 ("KVM: ARM: Memory virtualization setup") >>>>>> Cc: stable@vger.kernel.org # v3.10+ >>>>>> Cc: Marc Zyngier <marc.zyngier@arm.com> >>>>>> Cc: Christoffer Dall <christoffer.dall@linaro.org> >>>>>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> > > ... > >>> ok, then there's just the concern that we may be holding a spinlock for >>> a very long time. I seem to recall Mario once added something where he >>> unlocked and gave a chance to schedule something else for each PUD or >>> something like that, because he ran into the issue during migration. Am >>> I confusing this with something else? >> >> That definitely rings a bell: stage2_wp_range() uses that kind of trick >> to give the system a chance to breathe. Maybe we could use a similar >> trick in our S2 unmapping code? How about this (completely untested) patch: >> >> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c >> index 962616fd4ddd..1786c24212d4 100644 >> --- a/arch/arm/kvm/mmu.c >> +++ b/arch/arm/kvm/mmu.c >> @@ -292,8 +292,13 @@ static void unmap_stage2_range(struct kvm *kvm, phys_addr_t start, u64 size) >> phys_addr_t addr = start, end = start + size; >> phys_addr_t next; >> >> + BUG_ON(!spin_is_locked(&kvm->mmu_lock)); >> + >> pgd = kvm->arch.pgd + stage2_pgd_index(addr); >> do { >> + if (need_resched() || spin_needbreak(&kvm->mmu_lock)) >> + cond_resched_lock(&kvm->mmu_lock); > > nit: I think we could make the cond_resched_lock() unconditionally here: > Given, __cond_resched_lock() already does all the above checks : > > kernel/sched/core.c: > > int __cond_resched_lock(spinlock_t *lock) > { > int resched = should_resched(PREEMPT_LOCK_OFFSET); > > ... > > if (spin_needbreak(lock) || resched) { Right. And should_resched() also contains a test for need_resched(). This means we can also simplify stage2_wp_range(). Awesome! Thanks, M.
diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c index 962616fd4ddd..1786c24212d4 100644 --- a/arch/arm/kvm/mmu.c +++ b/arch/arm/kvm/mmu.c @@ -292,8 +292,13 @@ static void unmap_stage2_range(struct kvm *kvm, phys_addr_t start, u64 size) phys_addr_t addr = start, end = start + size; phys_addr_t next; + BUG_ON(!spin_is_locked(&kvm->mmu_lock)); + pgd = kvm->arch.pgd + stage2_pgd_index(addr); do { + if (need_resched() || spin_needbreak(&kvm->mmu_lock)) + cond_resched_lock(&kvm->mmu_lock); + next = stage2_pgd_addr_end(addr, end); if (!stage2_pgd_none(*pgd)) unmap_stage2_puds(kvm, pgd, addr, next);