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Tue, 04 Aug 2026 05:30:40 -0700 (PDT) Message-ID: <25cf9c88-7589-4a5d-994d-45f488a3e00b@suse.com> Date: Tue, 4 Aug 2026 14:30:38 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Content-Language: en-US To: "xen-devel@lists.xenproject.org" Cc: Andrew Cooper , Julien Grall , Stefano Stabellini , Anthony PERARD , Michal Orzel From: Jan Beulich Subject: [PATCH] radix-tree: drop radix_tree_init_maxindex() 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 Content-Transfer-Encoding: quoted-printable X-purgate-ID: tlsNG-4011c0/1785846640-4A9D9CFC-F5BD7A87/0/0 X-purgate-type: clean X-purgate-size: 2590 X-ZohoMail-DKIM: pass (identity @suse.com) X-ZM-MESSAGEID: 1785846686778158500 Content-Type: text/plain; charset="utf-8" Radix trees are in principle usable as soon as memory allocation works. (Radix trees with only index 0 populated are usable even earlier.) If only there wasn't height_to_maxindex[], which is filled only by a pre-SMP initcall. The benefit of this array is rather limited - the calculations done by __maxindex() can as well be done by radix_tree_maxindex(); the overhead isn't all this high. Fixes: 21844b0e32e7 ("PCI multi-seg: introduce notion of PCI segments") Fixes: 8dc6738dbb3c ("Update radix-tree.[ch] from upstream Linux to gain RC= U awareness") Reported-by: Andrew Cooper Signed-off-by: Jan Beulich Reviewed-by: Andrew Cooper --- Two Fixes: tags because the use of a pre-SMP initcall was clearly setting up a trap for later code to fall into. I know for certain that I've seen logs of Xen running on multi-segment systems. I can't quite explain how that ended up working. --- a/xen/common/radix-tree.c +++ b/xen/common/radix-tree.c @@ -32,12 +32,6 @@ struct radix_tree_path { #define RADIX_TREE_MAX_PATH (DIV_ROUND_UP(RADIX_TREE_INDEX_BITS, \ RADIX_TREE_MAP_SHIFT)) =20 -/* - * The height_to_maxindex array needs to be one deeper than the maximum - * path as height 0 holds only 1 entry. - */ -static unsigned long height_to_maxindex[RADIX_TREE_MAX_PATH + 1] __read_mo= stly; - static inline void *ptr_to_indirect(void *ptr) { return (void *)((unsigned long)ptr | RADIX_TREE_INDIRECT_PTR); @@ -80,7 +74,16 @@ static void radix_tree_node_free(struct */ static inline unsigned long radix_tree_maxindex(unsigned int height) { - return height_to_maxindex[height]; + unsigned int width =3D height * RADIX_TREE_MAP_SHIFT; + int shift =3D RADIX_TREE_INDEX_BITS - width; + + if (shift < 0) + return ~0UL; + + if (shift >=3D BITS_PER_LONG) + return 0UL; + + return ~0UL >> shift; } =20 /* @@ -705,27 +708,3 @@ void radix_tree_init(struct radix_tree_r { *root =3D (struct radix_tree_root)RADIX_TREE_INIT(); } - -static __init unsigned long __maxindex(unsigned int height) -{ - unsigned int width =3D height * RADIX_TREE_MAP_SHIFT; - int shift =3D RADIX_TREE_INDEX_BITS - width; - - if (shift < 0) - return ~0UL; - if (shift >=3D BITS_PER_LONG) - return 0UL; - return ~0UL >> shift; -} - -static int __init cf_check radix_tree_init_maxindex(void) -{ - unsigned int i; - - for (i =3D 0; i < ARRAY_SIZE(height_to_maxindex); i++) - height_to_maxindex[i] =3D __maxindex(i); - - return 0; -} -/* pre-SMP just so it runs before 'normal' initcalls */ -presmp_initcall(radix_tree_init_maxindex);