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@xxxxxxxxxxxxxxx # v3.10+
> Cc: Paolo Bonzini <pbonzin@xxxxxxxxxx>
> Cc: Marc Zyngier <marc.zyngier@xxxxxxx>
> Cc: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> [ Avoid vCPU starvation and lockup detector warnings ]
> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
>
> ---
> 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
>