Certain VMMs such as crosvm have features (e.g. sandboxing, pmem) that depend on being able to map guest memory as MAP_SHARED. The current restriction on sharing MAP_SHARED pages with the guest is preventing the use of those features with MTE. Therefore, remove this restriction. To avoid races between multiple tasks attempting to clear tags on the same page, introduce a new page flag, PG_mte_tag_clearing, and test-set it atomically before beginning to clear tags on a page. If the flag was not initially set, spin until the other task has finished clearing the tags. Link: https://linux-review.googlesource.com/id/I05a57f546f2b4d9b008a08f5f03e9ba3c950fdcc Signed-off-by: Peter Collingbourne <pcc@xxxxxxxxxx> --- arch/arm64/include/asm/mte.h | 5 +++++ arch/arm64/kernel/mte.c | 13 +++++++++++- arch/arm64/kvm/mmu.c | 36 +++++++--------------------------- include/linux/page-flags.h | 1 + include/trace/events/mmflags.h | 7 ++++--- 5 files changed, 29 insertions(+), 33 deletions(-) diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h index aa523591a44e..f66f70194c76 100644 --- a/arch/arm64/include/asm/mte.h +++ b/arch/arm64/include/asm/mte.h @@ -19,6 +19,7 @@ #include <asm/pgtable-types.h> void mte_clear_page_tags(void *addr); +void mte_ensure_page_tags_cleared(struct page *page); unsigned long mte_copy_tags_from_user(void *to, const void __user *from, unsigned long n); unsigned long mte_copy_tags_to_user(void __user *to, void *from, @@ -37,6 +38,9 @@ void mte_free_tag_storage(char *storage); /* track which pages have valid allocation tags */ #define PG_mte_tagged PG_arch_2 +/* the page is or has been in the process of having its tags cleared */ +#define PG_mte_tag_clearing PG_arch_3 + void mte_zero_clear_page_tags(void *addr); void mte_sync_tags(pte_t old_pte, pte_t pte); void mte_copy_page_tags(void *kto, const void *kfrom); @@ -53,6 +57,7 @@ size_t mte_probe_user_range(const char __user *uaddr, size_t size); /* unused if !CONFIG_ARM64_MTE, silence the compiler */ #define PG_mte_tagged 0 +#define PG_mte_tag_clearing 0 static inline void mte_zero_clear_page_tags(void *addr) { diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c index f6b00743c399..8f9655053a9f 100644 --- a/arch/arm64/kernel/mte.c +++ b/arch/arm64/kernel/mte.c @@ -57,7 +57,18 @@ static void mte_sync_page_tags(struct page *page, pte_t old_pte, * the new page->flags are visible before the tags were updated. */ smp_wmb(); - mte_clear_page_tags(page_address(page)); + mte_ensure_page_tags_cleared(page); +} + +void mte_ensure_page_tags_cleared(struct page *page) +{ + if (test_and_set_bit(PG_mte_tag_clearing, &page->flags)) { + while (!test_bit(PG_mte_tagged, &page->flags)) + ; + } else { + mte_clear_page_tags(page_address(page)); + set_bit(PG_mte_tagged, &page->flags); + } } void mte_sync_tags(pte_t old_pte, pte_t pte) diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c index f5651a05b6a8..016d14c9d798 100644 --- a/arch/arm64/kvm/mmu.c +++ b/arch/arm64/kvm/mmu.c @@ -1050,11 +1050,9 @@ static int get_vma_page_shift(struct vm_area_struct *vma, unsigned long hva) * able to see the page's tags and therefore they must be initialised first. If * PG_mte_tagged is set, tags have already been initialised. * - * The race in the test/set of the PG_mte_tagged flag is handled by: - * - preventing VM_SHARED mappings in a memslot with MTE preventing two VMs - * racing to santise the same page - * - mmap_lock protects between a VM faulting a page in and the VMM performing - * an mprotect() to add VM_MTE + * The race in the test/set of the PG_mte_tagged flag is handled via the flag + * PG_mte_tag_clearing which is atomically test and set before beginning a tag + * initialization, and spinning on PG_mte_tagged if it was already set. */ static int sanitise_mte_tags(struct kvm *kvm, kvm_pfn_t pfn, unsigned long size) @@ -1074,12 +1072,9 @@ static int sanitise_mte_tags(struct kvm *kvm, kvm_pfn_t pfn, if (!page) return -EFAULT; - for (i = 0; i < nr_pages; i++, page++) { - if (!test_bit(PG_mte_tagged, &page->flags)) { - mte_clear_page_tags(page_address(page)); - set_bit(PG_mte_tagged, &page->flags); - } - } + for (i = 0; i < nr_pages; i++, page++) + if (!test_bit(PG_mte_tagged, &page->flags)) + mte_ensure_page_tags_cleared(page); return 0; } @@ -1092,7 +1087,6 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, bool write_fault, writable, force_pte = false; bool exec_fault; bool device = false; - bool shared; unsigned long mmu_seq; struct kvm *kvm = vcpu->kvm; struct kvm_mmu_memory_cache *memcache = &vcpu->arch.mmu_page_cache; @@ -1142,8 +1136,6 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, vma_shift = get_vma_page_shift(vma, hva); } - shared = (vma->vm_flags & VM_SHARED); - switch (vma_shift) { #ifndef __PAGETABLE_PMD_FOLDED case PUD_SHIFT: @@ -1263,11 +1255,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, } if (fault_status != FSC_PERM && !device && kvm_has_mte(kvm)) { - /* Check the VMM hasn't introduced a new VM_SHARED VMA */ - if (!shared) - ret = sanitise_mte_tags(kvm, pfn, vma_pagesize); - else - ret = -EFAULT; + ret = sanitise_mte_tags(kvm, pfn, vma_pagesize); if (ret) goto out_unlock; } @@ -1705,16 +1693,6 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm, if (!vma) break; - /* - * VM_SHARED mappings are not allowed with MTE to avoid races - * when updating the PG_mte_tagged page flag, see - * sanitise_mte_tags for more details. - */ - if (kvm_has_mte(kvm) && vma->vm_flags & VM_SHARED) { - ret = -EINVAL; - break; - } - if (vma->vm_flags & VM_PFNMAP) { /* IO region dirty page logging not allowed */ if (new->flags & KVM_MEM_LOG_DIRTY_PAGES) { diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index e66f7aa3191d..447cdd4b1311 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -134,6 +134,7 @@ enum pageflags { #endif #ifdef CONFIG_64BIT PG_arch_2, + PG_arch_3, #endif #ifdef CONFIG_KASAN_HW_TAGS PG_skip_kasan_poison, diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h index e87cb2b80ed3..ecf7ae0de3d8 100644 --- a/include/trace/events/mmflags.h +++ b/include/trace/events/mmflags.h @@ -92,9 +92,9 @@ #endif #ifdef CONFIG_64BIT -#define IF_HAVE_PG_ARCH_2(flag,string) ,{1UL << flag, string} +#define IF_HAVE_PG_ARCH_2_3(flag,string) ,{1UL << flag, string} #else -#define IF_HAVE_PG_ARCH_2(flag,string) +#define IF_HAVE_PG_ARCH_2_3(flag,string) #endif #ifdef CONFIG_KASAN_HW_TAGS @@ -130,7 +130,8 @@ IF_HAVE_PG_UNCACHED(PG_uncached, "uncached" ) \ IF_HAVE_PG_HWPOISON(PG_hwpoison, "hwpoison" ) \ IF_HAVE_PG_IDLE(PG_young, "young" ) \ IF_HAVE_PG_IDLE(PG_idle, "idle" ) \ -IF_HAVE_PG_ARCH_2(PG_arch_2, "arch_2" ) \ +IF_HAVE_PG_ARCH_2_3(PG_arch_2, "arch_2" ) \ +IF_HAVE_PG_ARCH_2_3(PG_arch_3, "arch_3" ) \ IF_HAVE_PG_SKIP_KASAN_POISON(PG_skip_kasan_poison, "skip_kasan_poison") #define show_page_flags(flags) \ -- 2.37.0.rc0.104.g0611611a94-goog _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
