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Thu, 11 Jun 2026 08:10:07 -0700 (PDT) Message-ID: Date: Thu, 11 Jun 2026 17:10:05 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/2] xen/x86: Change stub page allocation/free To: Jason Andryuk Cc: xen-devel@lists.xenproject.org, Andrew Cooper , Teddy Astie , =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= References: <20260609000638.121027-1-jason.andryuk@amd.com> <20260609000638.121027-3-jason.andryuk@amd.com> <085ebfb8-d76c-4a13-8b5b-130959b25b51@amd.com> Content-Language: en-US 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: <085ebfb8-d76c-4a13-8b5b-130959b25b51@amd.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-purgate-ID: tlsNG-d25034/1781190607-D9F6ACF5-24010A98/0/0 X-purgate-type: clean X-purgate-size: 1261 On 10.06.2026 17:23, Jason Andryuk wrote: > On 2026-06-10 11:01, Roger Pau Monné wrote: >> On Mon, Jun 08, 2026 at 08:06:38PM -0400, Jason Andryuk wrote: >>> --- a/xen/arch/x86/setup.c >>> +++ b/xen/arch/x86/setup.c >>> @@ -2089,8 +2089,7 @@ void asmlinkage __init noreturn __start_xen(void) >>>         init_idle_domain(); >>>   -    this_cpu(stubs.addr) = alloc_stub_page(smp_processor_id(), >>> -                                           &this_cpu(stubs).mfn); >>> +    this_cpu(stubs.addr) = assign_stub_page(0); >> >> Given stub pages is first used quite late in the boot process, the above >> arrays would better be dynamically allocated using xvmalloc_array(). > > Ok.  At some point I intended to dynamically allocate.  But x86 doesn't have num_possible_cpus(), and I thought num_present_cpus() wouldn't have the correct value.  nr_cpu_ids seemed close to the value, but then I convinced myself NR_CPUS would be okay. Not specific to this patch: Using NR_CPUS is almost never okay. It's a last resort if you need a static upper bound. But NR_CPUS can be _much_ larger than nr_cpu_ids, and hence arrays generally want dimensioning (allocating) by using the latter. Jan