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Tue, 21 May 2024 03:23:07 -0700 (PDT) Message-ID: Date: Tue, 21 May 2024 12:23:07 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 05/12] IOMMU: rename and re-type ats_enabled Content-Language: en-US To: =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= Cc: "xen-devel@lists.xenproject.org" , Paul Durrant References: <64b028be-2197-4951-ae5b-32f9eabfa84a@suse.com> <7f11ca06-9bed-443b-9c79-0e62b71a1f96@suse.com> <24d52bbb-1329-4f8a-81be-505a35969875@suse.com> <44af358a-9510-4056-826c-3be99dc25830@suse.com> From: Jan Beulich Autocrypt: addr=jbeulich@suse.com; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 21.05.2024 12:03, Roger Pau Monné wrote: > On Tue, May 21, 2024 at 08:21:35AM +0200, Jan Beulich wrote: >> On 20.05.2024 12:29, Roger Pau Monné wrote: >>> On Wed, May 15, 2024 at 12:07:50PM +0200, Jan Beulich wrote: >>>> On 06.05.2024 15:53, Roger Pau Monné wrote: >>>>> On Mon, May 06, 2024 at 03:20:38PM +0200, Jan Beulich wrote: >>>>>> On 06.05.2024 14:42, Roger Pau Monné wrote: >>>>>>> On Thu, Feb 15, 2024 at 11:15:39AM +0100, Jan Beulich wrote: >>>>>>>> @@ -196,7 +196,7 @@ static int __must_check amd_iommu_setup_ >>>>>>>> dte->sys_mgt = MASK_EXTR(ivrs_dev->device_flags, ACPI_IVHD_SYSTEM_MGMT); >>>>>>>> >>>>>>>> if ( use_ats(pdev, iommu, ivrs_dev) ) >>>>>>>> - dte->i = ats_enabled; >>>>>>>> + dte->i = true; >>>>>>> >>>>>>> Might be easier to just use: >>>>>>> >>>>>>> dte->i = use_ats(pdev, iommu, ivrs_dev); >>>>>> >>>>>> I'm hesitant here, as in principle we might be overwriting a "true" by >>>>>> "false" then. >>>>> >>>>> Hm, but that would be fine, what's the point in enabling the IOMMU to >>>>> reply to ATS requests if ATS is not enabled on the device? >>>>> >>>>> IOW: overwriting a "true" with a "false" seem like the correct >>>>> behavior if it's based on the output of use_ats(). >>>> >>>> I don't think so, unless there were flow guarantees excluding the possibility >>>> of taking this path twice without intermediately disabling the device again. >>>> Down from here the enabling of ATS is gated on use_ats(). Hence if, in an >>>> earlier invocation, we enabled ATS (and set dte->i), we wouldn't turn off ATS >>>> below (there's only code to turn it on), yet with what you suggest we'd clear >>>> dte->i. >>> >>> Please bear with me, I think I'm confused, why would use_ats(), and if >>> that's the case, don't we want to update dte->i so that it matches the >>> ATS state? >> >> I'm afraid I can't parse this. Maybe a result of incomplete editing? The >> topic is complex enough that I don't want to even try to guess what you >> may have meant to ask ... > > Oh, indeed, sorry, the full sentences should have been: > > Please bear with me, I think I'm confused, why would use_ats() return > different values for the same device? Right now it can't, yet in principle opt_ats could change value when wired up accordingly via hypfs. > And if that's the case, don't we want to update dte->i so that it > matches the ATS state signaled by use_ats()? That depends on what adjustment would be done besides changing the variable value, if that was to become runtime changeable. >>> Otherwise we would fail to disable IOMMU device address translation >>> support if ATS was disabled? >> >> I think the answer here is "no", but with the above I'm not really sure >> here, either. > > Given the current logic in use_ats() AFAICT the return value of that > function should not change for a given device? Right now it shouldn't, yes. I'm still a little hesitant to have callers make implications from that. Jan