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Tue, 12 Mar 2024 06:40:25 -0700 (PDT) Message-ID: <2f41ad83-6911-4838-905b-dfe44ccaf8cf@suse.com> Date: Tue, 12 Mar 2024 14:40:23 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] drivers/char: mark XHCI DMA buffers reserved in memory map Content-Language: en-US To: =?UTF-8?Q?Marek_Marczykowski-G=C3=B3recki?= Cc: =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= , xen-devel@lists.xenproject.org, Andrew Cooper , Wei Liu , George Dunlap , Julien Grall , Stefano Stabellini References: <20240311203431.342530-1-marmarek@invisiblethingslab.com> <6a80ceb6-cc2a-4d8f-9a66-70063923b0ea@suse.com> <2a04315c-7bb8-4985-8aca-bece9d0d535e@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 12.03.2024 14:22, Marek Marczykowski-Górecki wrote: > On Tue, Mar 12, 2024 at 02:09:14PM +0100, Marek Marczykowski-Górecki wrote: >> On Tue, Mar 12, 2024 at 01:38:53PM +0100, Jan Beulich wrote: >>> On 12.03.2024 13:02, Marek Marczykowski-Górecki wrote: >>>> BTW should e820_change_range_type() return 1 in case of mapping already >>>> having the right type? Otherwise, if one wants to use >>>> iommu_add_extra_reserved_device_memory() on already reserved memory, the >>>> e820_change_range_type() would fail. >>> >>> You raised that question on Matrix yesterday, iirc, and I left it >>> unanswered there because it takes archeology to find the answer (or at >>> least get closer to one). And, please don't get me wrong, you could as >>> well do that yourself. (My vague recollection from having dealt with >>> similar code in Linux is that yes, in the example given the function >>> ought to indeed have failed back then. Depending on present uses etc >>> it may well be that we could reconsider, though.) >> >> I sure can do some archaeology there, I was just hoping any of you would >> know the answer already. > > None of the commit messages touching that code give the answer. But > looking around, most callers of reserve_e820_ram() ignore its return > value. One exception is reserving memory for kexec. I guess in that case > it may be intentional to fail if the area is reserved already, as it may > indicate it cannot be used for kexec. Is that correct? I suppose so, yes. > There are also a couple of calls to e820_change_range_type() in tboot > code where it changes E820_RESERVED to E820_UNUSABLE. There, I guess > changing e820_change_range_type() behavior would be okay. Possibly, but please don't put much trust in the tboot code we have. Jan