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Date: Wed, 9 Dec 2020 17:03:24 +0800
From: "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To: John Garry <john.garry@...wei.com>, <robin.murphy@....com>,
<joro@...tes.org>, <will@...nel.org>
CC: <linuxarm@...wei.com>, <linux-kernel@...r.kernel.org>,
<iommu@...ts.linux-foundation.org>, <xiyou.wangcong@...il.com>
Subject: Re: [RESEND PATCH v3 2/4] iommu/iova: Avoid double-negatives in
magazine helpers
On 2020/11/17 18:25, John Garry wrote:
> A similar crash to the following could be observed if initial CPU rcache
> magazine allocations fail in init_iova_rcaches():
>
> Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
> Mem abort info:
> ESR = 0x96000004
> EC = 0x25: DABT (current EL), IL = 32 bits
> SET = 0, FnV = 0
> EA = 0, S1PTW = 0
> Data abort info:
> ISV = 0, ISS = 0x00000004
> CM = 0, WnR = 0
> [0000000000000000] user address but active_mm is swapper
> Internal error: Oops: 96000004 [#1] PREEMPT SMP
> Modules linked in:
> CPU: 11 PID: 696 Comm: irq/40-hisi_sas Not tainted 5.9.0-rc7-dirty #109
> Hardware name: Huawei D06 /D06, BIOS Hisilicon D06 UEFI RC0 - V1.16.01 03/15/2019
> Call trace:
> free_iova_fast+0xfc/0x280
> iommu_dma_free_iova+0x64/0x70
> __iommu_dma_unmap+0x9c/0xf8
> iommu_dma_unmap_sg+0xa8/0xc8
> dma_unmap_sg_attrs+0x28/0x50
> cq_thread_v3_hw+0x2dc/0x528
> irq_thread_fn+0x2c/0xa0
> irq_thread+0x130/0x1e0
> kthread+0x154/0x158
> ret_from_fork+0x10/0x34
>
> Code: f9400060 f102001f 54000981 d4210000 (f9400043)
>
> ---[ end trace 4afcbdfc61b60467 ]---
>
> The issue is that expression !iova_magazine_full(NULL) evaluates true; this
> falls over in in __iova_rcache_insert() when we attempt to cache a mag
> and cpu_rcache->loaded == NULL:
>
> if (!iova_magazine_full(cpu_rcache->loaded)) {
> can_insert = true;
> ...
>
> if (can_insert)
> iova_magazine_push(cpu_rcache->loaded, iova_pfn);
>
> As above, can_insert is evaluated true, which it shouldn't be, and we try
> to insert pfns in a NULL mag, which is not safe.
>
> To avoid this, stop using double-negatives, like !iova_magazine_full() and
> !iova_magazine_empty(), and use positive tests, like
> iova_magazine_has_space() and iova_magazine_has_pfns(), respectively; these
> can safely deal with cpu_rcache->{loaded, prev} = NULL.
>
> Signed-off-by: John Garry <john.garry@...wei.com>
> ---
> drivers/iommu/iova.c | 29 +++++++++++++++++------------
> 1 file changed, 17 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
> index 81b7399dd5e8..1f3f0f8b12e0 100644
> --- a/drivers/iommu/iova.c
> +++ b/drivers/iommu/iova.c
> @@ -827,14 +827,18 @@ iova_magazine_free_pfns(struct iova_magazine *mag, struct iova_domain *iovad)
> mag->size = 0;
> }
>
> -static bool iova_magazine_full(struct iova_magazine *mag)
> +static bool iova_magazine_has_space(struct iova_magazine *mag)
> {
> - return (mag && mag->size == IOVA_MAG_SIZE);
> + if (!mag)
> + return false;
> + return mag->size < IOVA_MAG_SIZE;
> }
>
> -static bool iova_magazine_empty(struct iova_magazine *mag)
> +static bool iova_magazine_has_pfns(struct iova_magazine *mag)
> {
> - return (!mag || mag->size == 0);
> + if (!mag)
> + return false;
> + return mag->size;
> }
>
> static unsigned long iova_magazine_pop(struct iova_magazine *mag,
> @@ -843,7 +847,7 @@ static unsigned long iova_magazine_pop(struct iova_magazine *mag,
> int i;
> unsigned long pfn;
>
> - BUG_ON(iova_magazine_empty(mag));
> + BUG_ON(!iova_magazine_has_pfns(mag));
>
> /* Only fall back to the rbtree if we have no suitable pfns at all */
> for (i = mag->size - 1; mag->pfns[i] > limit_pfn; i--)
> @@ -859,7 +863,7 @@ static unsigned long iova_magazine_pop(struct iova_magazine *mag,
>
> static void iova_magazine_push(struct iova_magazine *mag, unsigned long pfn)
> {
> - BUG_ON(iova_magazine_full(mag));
> + BUG_ON(!iova_magazine_has_space(mag));
>
> mag->pfns[mag->size++] = pfn;
> }
> @@ -905,9 +909,9 @@ static bool __iova_rcache_insert(struct iova_domain *iovad,
> cpu_rcache = raw_cpu_ptr(rcache->cpu_rcaches);
> spin_lock_irqsave(&cpu_rcache->lock, flags);
>
> - if (!iova_magazine_full(cpu_rcache->loaded)) {
> + if (iova_magazine_has_space(cpu_rcache->loaded)) {
> can_insert = true;
> - } else if (!iova_magazine_full(cpu_rcache->prev)) {
> + } else if (iova_magazine_has_space(cpu_rcache->prev)) {
> swap(cpu_rcache->prev, cpu_rcache->loaded);
> can_insert = true;
> } else {
> @@ -916,8 +920,9 @@ static bool __iova_rcache_insert(struct iova_domain *iovad,
> if (new_mag) {
> spin_lock(&rcache->lock);
> if (rcache->depot_size < MAX_GLOBAL_MAGS) {
> - rcache->depot[rcache->depot_size++] =
> - cpu_rcache->loaded;
> + if (cpu_rcache->loaded)
Looks like it just needs to change this place. Compiler ensures that mag->size
will not be accessed when mag is NULL.
static bool iova_magazine_full(struct iova_magazine *mag)
{
return (mag && mag->size == IOVA_MAG_SIZE);
}
static bool iova_magazine_empty(struct iova_magazine *mag)
{
return (!mag || mag->size == 0);
}
> + rcache->depot[rcache->depot_size++] =
> + cpu_rcache->loaded;
> } else {
> mag_to_free = cpu_rcache->loaded;
> }
> @@ -968,9 +973,9 @@ static unsigned long __iova_rcache_get(struct iova_rcache *rcache,
> cpu_rcache = raw_cpu_ptr(rcache->cpu_rcaches);
> spin_lock_irqsave(&cpu_rcache->lock, flags);
>
> - if (!iova_magazine_empty(cpu_rcache->loaded)) {
> + if (iova_magazine_has_pfns(cpu_rcache->loaded)) {
> has_pfn = true;
> - } else if (!iova_magazine_empty(cpu_rcache->prev)) {
> + } else if (iova_magazine_has_pfns(cpu_rcache->prev)) {
> swap(cpu_rcache->prev, cpu_rcache->loaded);
> has_pfn = true;
> } else {
>
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