From: Baolu Lu <baolu.lu@linux.intel.com>
To: Uros Bizjak <ubizjak@gmail.com>
Cc: baolu.lu@linux.intel.com, iommu@lists.linux.dev,
linux-kernel@vger.kernel.org,
David Woodhouse <dwmw2@infradead.org>,
Joerg Roedel <joro@8bytes.org>, Will Deacon <will@kernel.org>,
Robin Murphy <robin.murphy@arm.com>
Subject: Re: [PATCH 2/3] iommu/vt-d: Use try_cmpxchg64() in intel_pasid_get_entry()
Date: Thu, 23 May 2024 21:44:33 +0800 [thread overview]
Message-ID: <b100a3c4-e5c3-41da-8c02-3a4986b49eec@linux.intel.com> (raw)
In-Reply-To: <CAFULd4Z=YkV1Hbs4DikPBwO-6rg8tfDLGeacSCnfbC02E5y+Cg@mail.gmail.com>
On 2024/5/23 21:34, Uros Bizjak wrote:
>>> + if (!try_cmpxchg64(&dir[dir_index].val, &tmp,
>>> + (u64)virt_to_phys(entries) | PASID_PTE_PRESENT)) {
>> Above change will cause a dead loop during boot. It should be
> No, it is correct as written:
>
> if (cmpxchg64(*ptr, 0, new))
>
> can be written as:
>
> if (cmpxchg64(*ptr, 0, new) != 0)
>
> this is equivalent to:
>
> tmp = 0ULL;
> if (!try_cmpxchg64(*ptr, &tmp, new))
The return value of both cmpxchg64() and try_cmpxchg64() is the old
value that was loaded from the memory location, right?
If so,
if (cmpxchg64(*ptr, 0, new) != 0)
is not equivalent to
if (!try_cmpxchg64(*ptr, &tmp, new))
Best regards,
baolu
next prev parent reply other threads:[~2024-05-23 13:44 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-22 8:26 [PATCH 1/3] iommu/amd: Use try_cmpxchg64() in v2_alloc_pte() Uros Bizjak
2024-05-22 8:26 ` [PATCH 2/3] iommu/vt-d: Use try_cmpxchg64() in intel_pasid_get_entry() Uros Bizjak
2024-05-23 13:24 ` Baolu Lu
2024-05-23 13:34 ` Uros Bizjak
2024-05-23 13:44 ` Baolu Lu [this message]
2024-05-23 13:57 ` Uros Bizjak
2024-05-24 1:08 ` Baolu Lu
2024-05-24 1:09 ` Baolu Lu
2024-05-22 8:26 ` [PATCH 3/3] iommufd: Use atomic_long_try_cmpxchg() in incr_user_locked_vm() Uros Bizjak
2024-05-22 12:45 ` Jason Gunthorpe
2024-05-23 10:40 ` [PATCH 1/3] iommu/amd: Use try_cmpxchg64() in v2_alloc_pte() Vasant Hegde
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