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b=jhWGubsx0hIxnInyYVZYdjDxvK/3LN690IRGX/hPVDQ12pGBceWhjDIr1dr9OY/T1 Q7ayBE7zUnN78znoRQ7vBuB1al3NxIl2si3y3ShSlxUWuq8KR66IypraogmNMc5M5l QU2Xt7XeWsIEtMt4DcjNP4kiyqa47lmGTr5JARpIiycIanibdWK3hzIcum20n+FJPv 9JXWzZbd66GHQpiGGC/dmd72IWkytEsrJAPqIHMsNJV7IFWK0Tp3lWBKGs+QObnU40 vn4F57ofrTv4y9yD0mxitvAB/jYcuUfdAPiXA7LHHjybFg9FxtOl+jmPhi2kvx5smG CHbMsUcn+vFIw== Date: Mon, 3 Aug 2026 22:33:15 +0000 From: Yosry Ahmed To: Brendan Jackman Cc: Borislav Petkov , Dave Hansen , Peter Zijlstra , Andrew Morton , David Hildenbrand , Vlastimil Babka , Mike Rapoport , Wei Xu , Johannes Weiner , Zi Yan , Lorenzo Stoakes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, x86@kernel.org, Sumit Garg , Will Deacon , rientjes@google.com, "Kalyazin, Nikita" , patrick.roy@linux.dev, "Itazuri, Takahiro" , Andy Lutomirski , David Kaplan , Thomas Gleixner , Patrick Bellasi , Reiji Watanabe , Sean Christopherson Subject: Re: [PATCH v3 08/26] x86/mm: move LDT remap into mm-local region Message-ID: References: <20260726-page_alloc-unmapped-v3-0-6f5729aa9832@google.com> <20260726-page_alloc-unmapped-v3-8-6f5729aa9832@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260726-page_alloc-unmapped-v3-8-6f5729aa9832@google.com> X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: C7AAA100010 X-Stat-Signature: kwgi4nj3s6j39543u4nrudamte7e7d1q X-HE-Tag: 1785796398-985821 X-HE-Meta: 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 ZnEFogOD y5wE7l+F0r+CLwizgwFuNlfpbRDvHWbdiVF+fGU8D8gwSbAdzytT6ojVx9lz811AD/M5KAu/odmbsre/LU2PPW8WXm8fFsydK07ykT0XUK54YME8drN9TLF6RdAYlg1+EwTDpgOYNY4EDGjJ8fK60AwybMhw7EKUMrAaGgWhFyb8qRqD6V/n61TSU+stnTb2PSCS7HSXdLUqCWV/s5d+cCoTdGC51RqbwErlW2kh0F2Mv+OBrlzW+kT+5aE8FwMTskIIUaEMtuxXvXn3+HmDDjp0XGftE5p4LumeAsyl2aJVEYjE1v/c+WlFzyA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, Jul 26, 2026 at 10:22:41PM +0000, Brendan Jackman wrote: > Now that x86 processes have a general mm-local region, the LDT-specific > management of the higher-level pagetables can mostly be replaced by just > using the generic mm-local API. > > Drop all management of pagetable allocation and freeing; that is now > handled automatically by virtue of the pagetables being in the mm-local > region. > > Drop explicit logic to map LDTs into the user pagetables under PTI; that > also happens automatically for this region. > > Unify the sanity-checking logic between x86_64 and PAE: use the generic > set_memory.c mechanism to walk pagetables. This means the > sanity-checking is slightly more relaxed, since lookup_address_in_pgd() > is more flexible than pgd_to_pmd_walk(), but this seems to be worth it > for the simplified code. It means that ldt.c doesn't have to know about > the exact structure of the mm-local region's pagetables. > > Signed-off-by: Brendan Jackman > --- [..] > diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c > index 40c5bf97dd5cc..685664c1ee770 100644 > --- a/arch/x86/kernel/ldt.c > +++ b/arch/x86/kernel/ldt.c > @@ -186,10 +186,16 @@ static struct ldt_struct *alloc_ldt_struct(unsigned int num_entries) > > #ifdef CONFIG_MITIGATION_PAGE_TABLE_ISOLATION > > -static void do_sanity_check(struct mm_struct *mm, > - bool had_kernel_mapping, > - bool had_user_mapping) > +static void sanity_check_ldt_mapping(struct mm_struct *mm) > { > + pgd_t *k_pgd = pgd_offset(mm, LDT_BASE_ADDR); > + pgd_t *u_pgd = kernel_to_user_pgdp(k_pgd); > + unsigned int k_level, u_level; > + bool had_kernel_mapping, had_user_mapping; > + > + had_kernel_mapping = lookup_address_in_pgd(k_pgd, LDT_BASE_ADDR, &k_level); > + had_user_mapping = lookup_address_in_pgd(u_pgd, LDT_BASE_ADDR, &u_level); > + As mentioned in the previous patch, this patch is difficult to review with the current arrangement and patches 7 and 8 can probably be structured in a better way. The unification of sanity_check_ldt_mapping() by using lookup_address_in_pgd() can also be done separately as part of that. > if (mm->context.ldt) { > /* > * We already had an LDT. The top-level entry should already