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Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.15.1 Subject: Re: [PATCH v5 2/6] iommu/amd: Introduce helper function to update 256-bit DTE To: Suravee Suthikulpanit , linux-kernel@vger.kernel.org, iommu@lists.linux.dev Cc: joro@8bytes.org, robin.murphy@arm.com, vasant.hegde@amd.com, jgg@nvidia.com, kevin.tian@intel.com, jon.grimm@amd.com, santosh.shukla@amd.com, pandoh@google.com, kumaranand@google.com References: <20241007041353.4756-1-suravee.suthikulpanit@amd.com> <20241007041353.4756-3-suravee.suthikulpanit@amd.com> Content-Language: en-US From: Uros Bizjak In-Reply-To: <20241007041353.4756-3-suravee.suthikulpanit@amd.com> This is a multi-part message in MIME format. --------------DOSrrXCulbNPxmqX14qrO8oc Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 7. 10. 24 06:13, Suravee Suthikulpanit wrote: > + > /**************************************************************************** > * > * Helper functions > * > ****************************************************************************/ > > +static void write_dte_upper128(struct dev_table_entry *ptr, struct dev_table_entry *new) > +{ > + struct dev_table_entry old = {}; > + > + do { > + old.data128[1] = ptr->data128[1]; > + new->data[2] &= ~DTE_DATA2_INTR_MASK; > + new->data[2] |= old.data[2] & (DTE_DATA2_INTR_MASK | DTE_DATA2_RESV_MASK); > + } while (!try_cmpxchg128(&ptr->data128[1], &old.data128[1], new->data128[1])); Please note that try_cmpxchg inherently updates &old.data128[1] above on failure. There is no need to update value again in the loop. Please also note that the value from ptr->data128[1] should be read using READ_ONCE() to prevent compiler from merging, refetching or reordering the read. Currently, there is no READ_ONCE() implemented for __int128, so something like the attached patch should be used. Based on the above, the loop should be rewritten as: old.data128[1] = READ_ONCE(ptr->data128[1]); do { new->data[2] &= ~DTE_DATA2_INTR_MASK; new->data[2] |= old.data[2] & (DTE_DATA2_INTR_MASK | DTE_DATA2_RESV_MASK); } while (!try_cmpxchg128(&ptr->data128[1], &old.data128[1], new->data128[1])); > +} > + > +static void write_dte_lower128(struct dev_table_entry *ptr, struct dev_table_entry *new) > +{ > + struct dev_table_entry old = {}; > + > + /* > + * Need to preserve DTE[96:106], which can be set by information in IVRS table. > + * See set_dev_entry_from_acpi(). > + */ > + new->data[1] |= ptr->data[1] & DTE_FLAG_MASK; > + > + do { > + old.data128[0] = ptr->data128[0]; > + } while (!try_cmpxchg128(&ptr->data128[0], &old.data128[0], new->data128[0])); And this one as: old.data128[0] = READ_ONCE(ptr->data128[0]); do { } while (!try_cmpxchg128(&ptr->data128[0], &old.data128[0], new->data128[0])); Best regards, Uros. --------------DOSrrXCulbNPxmqX14qrO8oc Content-Type: text/plain; charset=UTF-8; name="p.diff.txt" Content-Disposition: attachment; filename="p.diff.txt" Content-Transfer-Encoding: base64 ZGlmZiAtLWdpdCBhL2luY2x1ZGUvYXNtLWdlbmVyaWMvcndvbmNlLmggYi9pbmNsdWRlL2Fz bS1nZW5lcmljL3J3b25jZS5oCmluZGV4IDhkMGE2MjgwZTk4Mi4uOGJmOTQyYWQ1ZWYzIDEw MDY0NAotLS0gYS9pbmNsdWRlL2FzbS1nZW5lcmljL3J3b25jZS5oCisrKyBiL2luY2x1ZGUv YXNtLWdlbmVyaWMvcndvbmNlLmgKQEAgLTMzLDcgKzMzLDcgQEAKICAqIChlLmcuIGEgdmly dHVhbCBhZGRyZXNzKSBhbmQgYSBzdHJvbmcgcHJldmFpbGluZyB3aW5kLgogICovCiAjZGVm aW5lIGNvbXBpbGV0aW1lX2Fzc2VydF9yd29uY2VfdHlwZSh0KQkJCQkJXAotCWNvbXBpbGV0 aW1lX2Fzc2VydChfX25hdGl2ZV93b3JkKHQpIHx8IHNpemVvZih0KSA9PSBzaXplb2YobG9u ZyBsb25nKSwJXAorCWNvbXBpbGV0aW1lX2Fzc2VydChfX25hdGl2ZV93b3JkKHQpIHx8IHNp emVvZih0KSA9PSBzaXplb2YoX19kd29yZF90eXBlKSwgXAogCQkiVW5zdXBwb3J0ZWQgYWNj ZXNzIHNpemUgZm9yIHtSRUFELFdSSVRFfV9PTkNFKCkuIikKIAogLyoKZGlmZiAtLWdpdCBh L2luY2x1ZGUvbGludXgvY29tcGlsZXJfdHlwZXMuaCBiL2luY2x1ZGUvbGludXgvY29tcGls ZXJfdHlwZXMuaAppbmRleCA5NGI4ZmVkZmIwNzcuLjg2MTVlOTFmNDhmZCAxMDA2NDQKLS0t IGEvaW5jbHVkZS9saW51eC9jb21waWxlcl90eXBlcy5oCisrKyBiL2luY2x1ZGUvbGludXgv Y29tcGlsZXJfdHlwZXMuaApAQCAtNDY5LDYgKzQ2OSwxMiBAQCBzdHJ1Y3QgZnRyYWNlX2xp a2VseV9kYXRhIHsKIAkJdW5zaWduZWQgdHlwZToJKHVuc2lnbmVkIHR5cGUpMCwJCQlcCiAJ CXNpZ25lZCB0eXBlOgkoc2lnbmVkIHR5cGUpMAogCisjaWZkZWYgX19TSVpFT0ZfSU5UMTI4 X18KKyNkZWZpbmUgX19kd29yZF90eXBlIF9faW50MTI4CisjZWxzZQorI2RlZmluZSBfX2R3 b3JkX3R5cGUgbG9uZyBsb25nCisjZW5kaWYKKwogI2RlZmluZSBfX3VucXVhbF9zY2FsYXJf dHlwZW9mKHgpIHR5cGVvZigJCQkJXAogCQlfR2VuZXJpYygoeCksCQkJCQkJXAogCQkJIGNo YXI6CShjaGFyKTAsCQkJCVwKQEAgLTQ3Niw3ICs0ODIsNyBAQCBzdHJ1Y3QgZnRyYWNlX2xp a2VseV9kYXRhIHsKIAkJCSBfX3NjYWxhcl90eXBlX3RvX2V4cHJfY2FzZXMoc2hvcnQpLAkJ XAogCQkJIF9fc2NhbGFyX3R5cGVfdG9fZXhwcl9jYXNlcyhpbnQpLAkJXAogCQkJIF9fc2Nh bGFyX3R5cGVfdG9fZXhwcl9jYXNlcyhsb25nKSwJCVwKLQkJCSBfX3NjYWxhcl90eXBlX3Rv X2V4cHJfY2FzZXMobG9uZyBsb25nKSwJXAorCQkJIF9fc2NhbGFyX3R5cGVfdG9fZXhwcl9j YXNlcyhfX2R3b3JkX3R5cGUpLAlcCiAJCQkgZGVmYXVsdDogKHgpKSkKIAogLyogSXMgdGhp cyB0eXBlIGEgbmF0aXZlIHdvcmQgc2l6ZSAtLSB1c2VmdWwgZm9yIGF0b21pYyBvcGVyYXRp b25zICovCg== --------------DOSrrXCulbNPxmqX14qrO8oc--