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Message-ID: <af4dc808-4103-3825-f26e-edcb38cac5c7@huawei.com>
Date: Wed, 9 Dec 2020 20:31:26 +0800
From: "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To: John Garry <john.garry@...wei.com>,
"robin.murphy@....com" <robin.murphy@....com>,
"joro@...tes.org" <joro@...tes.org>,
"will@...nel.org" <will@...nel.org>
CC: Linuxarm <linuxarm@...wei.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
"xiyou.wangcong@...il.com" <xiyou.wangcong@...il.com>
Subject: Re: [RESEND PATCH v3 2/4] iommu/iova: Avoid double-negatives in
magazine helpers
On 2020/12/9 19:39, John Garry wrote:
> On 09/12/2020 09:03, Leizhen (ThunderTown) wrote:
>>
>>
>> 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>
>
> Thanks for checking here...
>
>>> ---
>>> 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.
>
> Not sure about that. We would get a crash prior to touching this codepath:
>
> So if cpu_rcache->loaded == NULL at entry, then !iova_magazine_full(cpu_rcache->loaded (==NULL) ) evaluates true, * above, so can_insert is set true, and we then attempt iova_magazine_push(cpu_rcache->loaded (==NULL), iova_pfn), which is not safe.
>
> ok?
OK, I got it.
Reviewed-by: Zhen Lei <thunder.leizhen@...wei.com>
>
> Cheers,
> John
>
>>
>> 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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