From mboxrd@z Thu Jan 1 00:00:00 1970 From: Brijesh Singh Subject: Re: [RFC PATCH v2 14/32] x86: mm: Provide support to use memblock when spliting large pages Date: Thu, 6 Apr 2017 09:05:03 -0500 Message-ID: References: <148846752022.2349.13667498174822419498.stgit@brijesh-build-machine> <148846771545.2349.9373586041426414252.stgit@brijesh-build-machine> <20170310110657.hophlog2juw5hpzz@pd.tnic> <20170316182836.tyvxoeq56thtc4pd@pd.tnic> <20170317101737.icdois7sdmtutt6b@pd.tnic> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit Cc: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Paolo Bonzini Return-path: In-Reply-To: <20170317101737.icdois7sdmtutt6b@pd.tnic> Sender: owner-linux-mm@kvack.org List-Id: kvm.vger.kernel.org Hi Boris, On 03/17/2017 05:17 AM, Borislav Petkov wrote: > On Thu, Mar 16, 2017 at 11:25:36PM +0100, Paolo Bonzini wrote: >> The kvmclock memory is initially zero so there is no need for the >> hypervisor to allocate anything; the point of these patches is just to >> access the data in a natural way from Linux source code. > > I realize that. > >> I also don't really like the patch as is (plus it fails modpost), but >> IMO reusing __change_page_attr and __split_large_page is the right thing >> to do. > > Right, so teaching pageattr.c about memblock could theoretically come > around and bite us later when a page allocated with memblock gets freed > with free_page(). > > And looking at this more, we have all this kernel pagetable preparation > code down the init_mem_mapping() call and the pagetable setup in > arch/x86/mm/init_{32,64}.c > > And that code even does some basic page splitting. Oh and it uses > alloc_low_pages() which knows whether to do memblock reservation or the > common __get_free_pages() when slabs are up. > I looked into arch/x86/mm/init_{32,64}.c and as you pointed the file contains routines to do basic page splitting. I think it sufficient for our usage. I should be able to drop the memblock patch from the series and update the Patch 15 [1] to use the kernel_physical_mapping_init(). The kernel_physical_mapping_init() creates the page table mapping using default KERNEL_PAGE attributes, I tried to extend the function by passing 'bool enc' flags to hint whether to clr or set _PAGE_ENC when splitting the pages. The code did not looked clean hence I dropped that idea. Instead, I took the below approach. I did some runtime test and it seem to be working okay. [1] http://marc.info/?l=linux-mm&m=148846773731212&w=2 diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c index 7df5f4c..de16ef4 100644 --- a/arch/x86/mm/mem_encrypt.c +++ b/arch/x86/mm/mem_encrypt.c @@ -15,6 +15,7 @@ #include #include #include +#include #include #include @@ -22,6 +23,8 @@ #include #include +#include "mm_internal.h" + extern pmdval_t early_pmd_flags; int __init __early_make_pgtable(unsigned long, pmdval_t); void __init __early_pgtable_flush(void); @@ -258,6 +261,72 @@ static void sme_free(struct device *dev, size_t size, void *vaddr, swiotlb_free_coherent(dev, size, vaddr, dma_handle); } +static int __init early_set_memory_enc_dec(resource_size_t paddr, + unsigned long size, bool enc) +{ + pte_t *kpte; + int level; + unsigned long vaddr, vaddr_end, vaddr_next; + + vaddr = (unsigned long)__va(paddr); + vaddr_next = vaddr; + vaddr_end = vaddr + size; + + /* + * We are going to change the physical page attribute from C=1 to C=0. + * Flush the caches to ensure that all the data with C=1 is flushed to + * memory. Any caching of the vaddr after function returns will + * use C=0. + */ + clflush_cache_range(__va(paddr), size); + + for (; vaddr < vaddr_end; vaddr = vaddr_next) { + kpte = lookup_address(vaddr, &level); + if (!kpte || pte_none(*kpte) ) + return 1; + + if (level == PG_LEVEL_4K) { + pte_t new_pte; + unsigned long pfn = pte_pfn(*kpte); + pgprot_t new_prot = pte_pgprot(*kpte); + + if (enc) + pgprot_val(new_prot) |= _PAGE_ENC; + else + pgprot_val(new_prot) &= ~_PAGE_ENC; + + new_pte = pfn_pte(pfn, canon_pgprot(new_prot)); + pr_info(" pte %016lx -> 0x%016lx\n", pte_val(*kpte), + pte_val(new_pte)); + set_pte_atomic(kpte, new_pte); + vaddr_next = (vaddr & PAGE_MASK) + PAGE_SIZE; + continue; + } + + /* + * virtual address is part of large page, create the page + * table mapping to use smaller pages (4K). The virtual and + * physical address must be aligned to PMD level. + */ + kernel_physical_mapping_init(__pa(vaddr & PMD_MASK), + __pa((vaddr_end & PMD_MASK) + PMD_SIZE), + 0); + } + + __flush_tlb_all(); + return 0; +} + +int __init early_set_memory_decrypted(resource_size_t paddr, unsigned long size) +{ + return early_set_memory_enc_dec(paddr, size, false); +} + +int __init early_set_memory_encrypted(resource_size_t paddr, unsigned long size) +{ + return early_set_memory_enc_dec(paddr, size, true); +} + > So what would be much cleaner, IMHO, is if one would reuse that code to > change init_mm.pgd mappings early without copying pageattr.c. > > init_mem_mapping() gets called before kvm_guest_init() in setup_arch() > so the guest would simply fixup its pagetable right there. > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org