| Message ID | 1491228763-23450-1-git-send-email-suzuki.poulose@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi, On Mon, Apr 03, 2017 at 03:12:43PM +0100, 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. And since we have to unmap the entire Guest memory range > holding a spinlock, make sure we yield the lock if necessary, after we > unmap each PUD range. > > Fixes: commit d5d8184d35c9 ("KVM: ARM: Memory virtualization setup") > Cc: stable@vger.kernel.org # v3.10+ > Cc: Paolo Bonzini <pbonzin@redhat.com> > Cc: Marc Zyngier <marc.zyngier@arm.com> > Cc: Christoffer Dall <christoffer.dall@linaro.org> > Cc: Mark Rutland <mark.rutland@arm.com> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> > [ Avoid vCPU starvation and lockup detector warnings ] > Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> > > --- > Changes since V2: > - Restrict kvm->mmu_lock relaxation to bigger ranges in unmap_stage2_range(), > to avoid possible issues like [0] > > [0] http://lists.infradead.org/pipermail/linux-arm-kernel/2017-March/498210.html Sorry if I'm being thick, but how does restricting this to a larger range help with the "sleeping function called from invalid context" issue? Surely that just makes it rarer? Thanks, Mark. > > Changes since V1: > - Yield the kvm->mmu_lock if necessary in unmap_stage2_range to prevent > vCPU starvation and lockup detector warnings. > --- > arch/arm/kvm/mmu.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c > index 13b9c1f..db94f3a 100644 > --- a/arch/arm/kvm/mmu.c > +++ b/arch/arm/kvm/mmu.c > @@ -292,8 +292,15 @@ 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; > > + assert_spin_locked(&kvm->mmu_lock); > pgd = kvm->arch.pgd + stage2_pgd_index(addr); > do { > + /* > + * If the range is too large, release the kvm->mmu_lock > + * to prevent starvation and lockup detector warnings. > + */ > + if (size > S2_PUD_SIZE) > + 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); > @@ -831,7 +838,10 @@ 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); > + > /* Free the HW pgd, one page at a time */ > free_pages_exact(kvm->arch.pgd, S2_PGD_SIZE); > kvm->arch.pgd = NULL; > -- > 2.7.4 >
On 03/04/17 15:22, Mark Rutland wrote: > Hi, > > On Mon, Apr 03, 2017 at 03:12:43PM +0100, 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. And since we have to unmap the entire Guest memory range >> holding a spinlock, make sure we yield the lock if necessary, after we >> unmap each PUD range. >> >> Fixes: commit d5d8184d35c9 ("KVM: ARM: Memory virtualization setup") >> Cc: stable@vger.kernel.org # v3.10+ >> Cc: Paolo Bonzini <pbonzin@redhat.com> >> Cc: Marc Zyngier <marc.zyngier@arm.com> >> Cc: Christoffer Dall <christoffer.dall@linaro.org> >> Cc: Mark Rutland <mark.rutland@arm.com> >> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> >> [ Avoid vCPU starvation and lockup detector warnings ] >> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> >> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> >> >> --- >> Changes since V2: >> - Restrict kvm->mmu_lock relaxation to bigger ranges in unmap_stage2_range(), >> to avoid possible issues like [0] >> >> [0] http://lists.infradead.org/pipermail/linux-arm-kernel/2017-March/498210.html > > Sorry if I'm being thick, but how does restricting this to a larger > range help with the "sleeping function called from invalid context" > issue? > > Surely that just makes it rarer? The issue in [0] arises when we try to unmap a page at stage2, while holding a different spinlock and we try to do cond_resched_lock(), thinking we might spend too much time holding the lock. With this patch, we don't try to relax the lock if we are dealing with smaller sizes and hence avoids cond_resched_lock(). So in effect it tries to avoid the cond_resched_lock() when we could finish the operation soon enough. Hope that helps. Suzuki
On Mon, Apr 03, 2017 at 03:22:11PM +0100, Mark Rutland wrote: > Hi, > > On Mon, Apr 03, 2017 at 03:12:43PM +0100, 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. And since we have to unmap the entire Guest memory range > > holding a spinlock, make sure we yield the lock if necessary, after we > > unmap each PUD range. > > > > Fixes: commit d5d8184d35c9 ("KVM: ARM: Memory virtualization setup") > > Cc: stable@vger.kernel.org # v3.10+ > > Cc: Paolo Bonzini <pbonzin@redhat.com> > > Cc: Marc Zyngier <marc.zyngier@arm.com> > > Cc: Christoffer Dall <christoffer.dall@linaro.org> > > Cc: Mark Rutland <mark.rutland@arm.com> > > Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> > > [ Avoid vCPU starvation and lockup detector warnings ] > > Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> > > Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> > > > > --- > > Changes since V2: > > - Restrict kvm->mmu_lock relaxation to bigger ranges in unmap_stage2_range(), > > to avoid possible issues like [0] > > > > [0] http://lists.infradead.org/pipermail/linux-arm-kernel/2017-March/498210.html > > Sorry if I'm being thick, but how does restricting this to a larger > range help with the "sleeping function called from invalid context" > issue? > > Surely that just makes it rarer? As far as I can tell, the unmap_stage2_range() function is only called in the problematic path which has the extra lock taken rom try_to_unmap_one() via the kvm_unmap_hva() function, which always passes PAGE_SIZE as the argument, which is always smaller than S2_PUD_SIZE. Did I miss something? Thanks, -Christoffer > > > > > Changes since V1: > > - Yield the kvm->mmu_lock if necessary in unmap_stage2_range to prevent > > vCPU starvation and lockup detector warnings. > > --- > > arch/arm/kvm/mmu.c | 10 ++++++++++ > > 1 file changed, 10 insertions(+) > > > > diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c > > index 13b9c1f..db94f3a 100644 > > --- a/arch/arm/kvm/mmu.c > > +++ b/arch/arm/kvm/mmu.c > > @@ -292,8 +292,15 @@ 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; > > > > + assert_spin_locked(&kvm->mmu_lock); > > pgd = kvm->arch.pgd + stage2_pgd_index(addr); > > do { > > + /* > > + * If the range is too large, release the kvm->mmu_lock > > + * to prevent starvation and lockup detector warnings. > > + */ > > + if (size > S2_PUD_SIZE) > > + 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); > > @@ -831,7 +838,10 @@ 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); > > + > > /* Free the HW pgd, one page at a time */ > > free_pages_exact(kvm->arch.pgd, S2_PGD_SIZE); > > kvm->arch.pgd = NULL; > > -- > > 2.7.4 > >
diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c index 13b9c1f..db94f3a 100644 --- a/arch/arm/kvm/mmu.c +++ b/arch/arm/kvm/mmu.c @@ -292,8 +292,15 @@ 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; + assert_spin_locked(&kvm->mmu_lock); pgd = kvm->arch.pgd + stage2_pgd_index(addr); do { + /* + * If the range is too large, release the kvm->mmu_lock + * to prevent starvation and lockup detector warnings. + */ + if (size > S2_PUD_SIZE) + 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); @@ -831,7 +838,10 @@ 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); + /* Free the HW pgd, one page at a time */ free_pages_exact(kvm->arch.pgd, S2_PGD_SIZE); kvm->arch.pgd = NULL;
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. And since we have to unmap the entire Guest memory range holding a spinlock, make sure we yield the lock if necessary, after we unmap each PUD range. Fixes: commit d5d8184d35c9 ("KVM: ARM: Memory virtualization setup") Cc: stable@vger.kernel.org # v3.10+ Cc: Paolo Bonzini <pbonzin@redhat.com> Cc: Marc Zyngier <marc.zyngier@arm.com> Cc: Christoffer Dall <christoffer.dall@linaro.org> Cc: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> [ Avoid vCPU starvation and lockup detector warnings ] Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> --- Changes since V2: - Restrict kvm->mmu_lock relaxation to bigger ranges in unmap_stage2_range(), to avoid possible issues like [0] [0] http://lists.infradead.org/pipermail/linux-arm-kernel/2017-March/498210.html Changes since V1: - Yield the kvm->mmu_lock if necessary in unmap_stage2_range to prevent vCPU starvation and lockup detector warnings. --- arch/arm/kvm/mmu.c | 10 ++++++++++ 1 file changed, 10 insertions(+)