[PATCH 2/2] KVM: arm/arm64: vgic-its: Take the srcu lock when parsing the memslots

Auger Eric eric.auger at redhat.com
Tue Mar 19 08:17:34 PDT 2019


Hi Marc,

On 3/19/19 2:30 PM, Marc Zyngier wrote:
> Calling kvm_is_visible_gfn() implies that we're parsing the memslots,
> and doing this without the srcu lock is frown upon:
> 
> [12704.164532] =============================
> [12704.164544] WARNING: suspicious RCU usage
> [12704.164560] 5.1.0-rc1-00008-g600025238f51-dirty #16 Tainted: G        W
> [12704.164573] -----------------------------
> [12704.164589] ./include/linux/kvm_host.h:605 suspicious rcu_dereference_check() usage!
> [12704.164602] other info that might help us debug this:
> [12704.164616] rcu_scheduler_active = 2, debug_locks = 1
> [12704.164631] 6 locks held by qemu-system-aar/13968:
> [12704.164644]  #0: 000000007ebdae4f (&kvm->lock){+.+.}, at: vgic_its_set_attr+0x244/0x3a0
> [12704.164691]  #1: 000000007d751022 (&its->its_lock){+.+.}, at: vgic_its_set_attr+0x250/0x3a0
> [12704.164726]  #2: 00000000219d2706 (&vcpu->mutex){+.+.}, at: lock_all_vcpus+0x64/0xd0
> [12704.164761]  #3: 00000000a760aecd (&vcpu->mutex){+.+.}, at: lock_all_vcpus+0x64/0xd0
> [12704.164794]  #4: 000000000ef8e31d (&vcpu->mutex){+.+.}, at: lock_all_vcpus+0x64/0xd0
> [12704.164827]  #5: 000000007a872093 (&vcpu->mutex){+.+.}, at: lock_all_vcpus+0x64/0xd0
> [12704.164861] stack backtrace:
> [12704.164878] CPU: 2 PID: 13968 Comm: qemu-system-aar Tainted: G        W         5.1.0-rc1-00008-g600025238f51-dirty #16
> [12704.164887] Hardware name: rockchip evb_rk3399/evb_rk3399, BIOS 2019.04-rc3-00124-g2feec69fb1 03/15/2019
> [12704.164896] Call trace:
> [12704.164910]  dump_backtrace+0x0/0x138
> [12704.164920]  show_stack+0x24/0x30
> [12704.164934]  dump_stack+0xbc/0x104
> [12704.164946]  lockdep_rcu_suspicious+0xcc/0x110
> [12704.164958]  gfn_to_memslot+0x174/0x190
> [12704.164969]  kvm_is_visible_gfn+0x28/0x70
> [12704.164980]  vgic_its_check_id.isra.0+0xec/0x1e8
> [12704.164991]  vgic_its_save_tables_v0+0x1ac/0x330
> [12704.165001]  vgic_its_set_attr+0x298/0x3a0
> [12704.165012]  kvm_device_ioctl_attr+0x9c/0xd8
> [12704.165022]  kvm_device_ioctl+0x8c/0xf8
> [12704.165035]  do_vfs_ioctl+0xc8/0x960
> [12704.165045]  ksys_ioctl+0x8c/0xa0
> [12704.165055]  __arm64_sys_ioctl+0x28/0x38
> [12704.165067]  el0_svc_common+0xd8/0x138
> [12704.165078]  el0_svc_handler+0x38/0x78
> [12704.165089]  el0_svc+0x8/0xc
> 
> Make sure the lock is taken when doing this.
> 
> Fixes: bf308242ab98 ("KVM: arm/arm64: VGIC/ITS: protect kvm_read_guest() calls with SRCU lock")
> Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>
Reviewed-by: Eric Auger <eric.auger at redhat.com>

Thanks

Eric
> ---
>  virt/kvm/arm/vgic/vgic-its.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> index bb76220f2f30..7543f166943d 100644
> --- a/virt/kvm/arm/vgic/vgic-its.c
> +++ b/virt/kvm/arm/vgic/vgic-its.c
> @@ -880,8 +880,9 @@ static bool vgic_its_check_id(struct vgic_its *its, u64 baser, u32 id,
>  	u64 indirect_ptr, type = GITS_BASER_TYPE(baser);
>  	phys_addr_t base = GITS_BASER_ADDR_48_to_52(baser);
>  	int esz = GITS_BASER_ENTRY_SIZE(baser);
> -	int index;
> +	int index, idx;
>  	gfn_t gfn;
> +	bool ret;
>  
>  	switch (type) {
>  	case GITS_BASER_TYPE_DEVICE:
> @@ -908,7 +909,8 @@ static bool vgic_its_check_id(struct vgic_its *its, u64 baser, u32 id,
>  
>  		if (eaddr)
>  			*eaddr = addr;
> -		return kvm_is_visible_gfn(its->dev->kvm, gfn);
> +
> +		goto out;
>  	}
>  
>  	/* calculate and check the index into the 1st level */
> @@ -938,7 +940,12 @@ static bool vgic_its_check_id(struct vgic_its *its, u64 baser, u32 id,
>  
>  	if (eaddr)
>  		*eaddr = indirect_ptr;
> -	return kvm_is_visible_gfn(its->dev->kvm, gfn);
> +
> +out:
> +	idx = srcu_read_lock(&its->dev->kvm->srcu);
> +	ret = kvm_is_visible_gfn(its->dev->kvm, gfn);
> +	srcu_read_unlock(&its->dev->kvm->srcu, idx);
> +	return ret;
>  }
>  
>  static int vgic_its_alloc_collection(struct vgic_its *its,
> 



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