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Date: Sun, 7 Jan 2018 18:35:56 +0800 From: Jike Song <albcamus@...il.com> To: Thomas Gleixner <tglx@...utronix.de> Cc: luto@...nel.org, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] x86/mm/pti: remove dead logic during user pagetable population On Sun, Jan 7, 2018 at 5:48 PM, Thomas Gleixner <tglx@...utronix.de> wrote: > On Sun, 7 Jan 2018, Jike Song wrote: >> On Sun, Jan 7, 2018 at 3:33 AM, Thomas Gleixner <tglx@...utronix.de> wrote: >> > On Sun, 7 Jan 2018, Jike Song wrote: >> > >> > Care to explain why you think this is not needed? >> > >> >> Hi Thomas, >> >> Look at one of the original code snippets: >> >> 162 if (pgd_none(*pgd)) { >> 163 unsigned long new_p4d_page = __get_free_page(gfp); >> 164 if (!new_p4d_page) >> 165 return NULL; >> 166 >> 167 if (pgd_none(*pgd)) { >> 168 set_pgd(pgd, __pgd(_KERNPG_TABLE | >> __pa(new_p4d_page))); >> 169 new_p4d_page = 0; >> 170 } >> 171 if (new_p4d_page) >> 172 free_page(new_p4d_page); >> 173 } >> >> Correct me if I'm too dumb to see the rationale here, but to me there >> can't be any difference between >> two pgd_none(*pgd) of L162 and L167, so it is always false in L171. > > Right, but this kind of explanation wants to be in the changelog. Empty > changelogs for this kind of change are just not acceptable. > Roger that, just sent v2 out :) I'm not quite sure but I CCed stable@...nel.org anyway. > Thanks, > > tglx -- Thanks, Jike
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