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Date: Sun, 2 Aug 2020 17:55:55 -0700 From: Atish Patra <atishp@...shpatra.org> To: Mike Rapoport <rppt@...nel.org> Cc: Atish Patra <atish.patra@....com>, "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>, Anup Patel <anup.patel@....com>, Ard Biesheuvel <ardb@...nel.org>, Arvind Sankar <nivedita@...m.mit.edu>, Greentime Hu <greentime.hu@...ive.com>, Ingo Molnar <mingo@...nel.org>, Kees Cook <keescook@...omium.org>, linux-efi <linux-efi@...r.kernel.org>, linux-riscv <linux-riscv@...ts.infradead.org>, Mark Rutland <mark.rutland@....com>, Masahiro Yamada <masahiroy@...nel.org>, Nick Hu <nickhu@...estech.com>, Palmer Dabbelt <palmer@...belt.com>, "Paul E. McKenney" <paulmck@...nel.org>, Paul Walmsley <paul.walmsley@...ive.com>, Thomas Gleixner <tglx@...utronix.de>, Will Deacon <will@...nel.org>, Yash Shah <yash.shah@...ive.com>, Zong Li <zong.li@...ive.com> Subject: Re: [RFT PATCH v4 3/9] RISC-V: Implement late mapping page table allocation functions On Thu, Jul 30, 2020 at 2:14 AM Mike Rapoport <rppt@...nel.org> wrote: > > Hi, > > On Wed, Jul 29, 2020 at 04:36:29PM -0700, Atish Patra wrote: > > Currently, page table setup is done during setup_va_final where fixmap can > > be used to create the temporary mappings. The physical frame is allocated > > from memblock_alloc_* functions. However, this won't work if page table > > mapping needs to be created for a different mm context (i.e. efi mm) at > > a later point of time. > > TBH, I'm not very happy to see pte/pmd allocations, but I don't see a > way to reuse the existing routines in this case. > > As a general wild idea, maybe it's worth using something like > > struct pt_alloc_ops { > pte_t *(*get_pte_virt)(phys_addr_t pa); > phys_addr_t (*alloc_pte)(uintptr_t va); > ... > }; > > and add there implementations: nommu, MMU early and MMU late. > Yeah. That will be much cleaner. Thanks. I will change it to have function pointers instead of if else blocks. > Some more comments below. > > > Use generic kernel page allocation function & macros for any mapping > > after setup_vm_final. > > > > Signed-off-by: Atish Patra <atish.patra@....com> > > --- > > arch/riscv/mm/init.c | 29 ++++++++++++++++++++++++----- > > 1 file changed, 24 insertions(+), 5 deletions(-) > > > > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c > > index 68c608a0e91f..cba03fec08c1 100644 > > --- a/arch/riscv/mm/init.c > > +++ b/arch/riscv/mm/init.c > > @@ -212,6 +212,7 @@ pgd_t swapper_pg_dir[PTRS_PER_PGD] __page_aligned_bss; > > pgd_t trampoline_pg_dir[PTRS_PER_PGD] __page_aligned_bss; > > pte_t fixmap_pte[PTRS_PER_PTE] __page_aligned_bss; > > static bool mmu_enabled; > > +static bool late_mapping; > > > > #define MAX_EARLY_MAPPING_SIZE SZ_128M > > > > @@ -236,7 +237,9 @@ void __set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t prot) > > > > static pte_t *__init get_pte_virt(phys_addr_t pa) > > { > > - if (mmu_enabled) { > > + if (late_mapping) > > + return (pte_t *) __va(pa); > > + else if (mmu_enabled) { > > clear_fixmap(FIX_PTE); > > return (pte_t *)set_fixmap_offset(FIX_PTE, pa); > > } else { > > @@ -246,13 +249,19 @@ static pte_t *__init get_pte_virt(phys_addr_t pa) > > > > static phys_addr_t __init alloc_pte(uintptr_t va) > > { > > + unsigned long vaddr; > > /* > > * We only create PMD or PGD early mappings so we > > * should never reach here with MMU disabled. > > */ > > BUG_ON(!mmu_enabled); > > - > > - return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE); > > + if (late_mapping) { > > + vaddr = __get_free_page(GFP_KERNEL); > > + if (!vaddr || !pgtable_pte_page_ctor(virt_to_page(vaddr))) > > + BUG(); > > Is BUG() here really necessary? If I understand correctly, this would be > used to enable mappings for EFI runtime services, so we probably want to > propagete the error to to caller and, if really necessary, BUG() there, > don't we? > If __get_free_page is failing here, something is seriously wrong and the system should panic. But I agree with you that this should happen in the caller rather than the callee. We need to change the signature of each create_*_mapping function in order to propagate the error to the caller. Do you see any issues with that ? As it will affect page table allocation for all three cases, should we consolidate all the BUG() cases in caller only ? > > + return __pa(vaddr); > > + } else > > + return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE); > > } > > > > static void __init create_pte_mapping(pte_t *ptep, > > @@ -281,7 +290,9 @@ pmd_t early_pmd[PTRS_PER_PMD * NUM_EARLY_PMDS] __initdata __aligned(PAGE_SIZE); > > > > static pmd_t *__init get_pmd_virt(phys_addr_t pa) > > { > > - if (mmu_enabled) { > > + if (late_mapping) > > + return (pmd_t *) __va(pa); > > + else if (mmu_enabled) { > > clear_fixmap(FIX_PMD); > > return (pmd_t *)set_fixmap_offset(FIX_PMD, pa); > > } else { > > @@ -292,8 +303,13 @@ static pmd_t *__init get_pmd_virt(phys_addr_t pa) > > static phys_addr_t __init alloc_pmd(uintptr_t va) > > { > > uintptr_t pmd_num; > > + unsigned long vaddr; > > > > - if (mmu_enabled) > > + if (late_mapping) { > > + vaddr = __get_free_page(GFP_KERNEL); > > + BUG_ON(!vaddr); > > + return __pa(vaddr); > > Does nommu also need to allocate a page for pmd? > Not sure if I understand the question correctly. Before MMU is enabled, we are using statically allocated early_pmd. > > + } else if (mmu_enabled) > > return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE); > > > > pmd_num = (va - PAGE_OFFSET) >> PGDIR_SHIFT; > > @@ -533,6 +549,9 @@ static void __init setup_vm_final(void) > > /* Move to swapper page table */ > > csr_write(CSR_SATP, PFN_DOWN(__pa_symbol(swapper_pg_dir)) | SATP_MODE); > > local_flush_tlb_all(); > > + > > + /* generic page allocation function must be used to setup page table */ > > + late_mapping = true; > > } > > #else > > asmlinkage void __init setup_vm(uintptr_t dtb_pa) > > -- > > 2.24.0 > > > > -- > Sincerely yours, > Mike. -- Regards, Atish
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