[v3,2/2] s390/mm: re-enable the shared zeropage for !PV and !skeys KVM guests

Message ID	20240411161441.910170-3-david@redhat.com (mailing list archive)
State	New
Headers	show Return-Path: <owner-linux-mm@kvack.org> From: David Hildenbrand <david@redhat.com> To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, David Hildenbrand <david@redhat.com>, Christian Borntraeger <borntraeger@linux.ibm.com>, Janosch Frank <frankja@linux.ibm.com>, Claudio Imbrenda <imbrenda@linux.ibm.com>, Heiko Carstens <hca@linux.ibm.com>, Vasily Gorbik <gor@linux.ibm.com>, Andrew Morton <akpm@linux-foundation.org>, Peter Xu <peterx@redhat.com>, Alexander Gordeev <agordeev@linux.ibm.com>, Sven Schnelle <svens@linux.ibm.com>, Gerald Schaefer <gerald.schaefer@linux.ibm.com>, Andrea Arcangeli <aarcange@redhat.com>, kvm@vger.kernel.org, linux-s390@vger.kernel.org Subject: [PATCH v3 2/2] s390/mm: re-enable the shared zeropage for !PV and !skeys KVM guests Date: Thu, 11 Apr 2024 18:14:41 +0200 Message-ID: <20240411161441.910170-3-david@redhat.com> In-Reply-To: <20240411161441.910170-1-david@redhat.com> References: <20240411161441.910170-1-david@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org Precedence: bulk
Series	s390/mm: shared zeropage + KVM fixes \| expand [v3,0/2] s390/mm: shared zeropage + KVM fixes [v3,1/2] mm/userfaultfd: don't place zeropages when zeropages are disallowed [v3,2/2] s390/mm: re-enable the shared zeropage for !PV and !skeys KVM guests

diff --git a/arch/s390/include/asm/gmap.h b/arch/s390/include/asm/gmap.h index 5cc46e0dde62..9725586f4259 100644 --- a/arch/s390/include/asm/gmap.h +++ b/arch/s390/include/asm/gmap.h @@ -146,7 +146,7 @@ int gmap_mprotect_notify(struct gmap *, unsigned long start, void gmap_sync_dirty_log_pmd(struct gmap *gmap, unsigned long dirty_bitmap[4], unsigned long gaddr, unsigned long vmaddr); -int gmap_mark_unmergeable(void); +int s390_disable_cow_sharing(void); void s390_unlist_old_asce(struct gmap *gmap); int s390_replace_asce(struct gmap *gmap); void s390_uv_destroy_pfns(unsigned long count, unsigned long *pfns); diff --git a/arch/s390/include/asm/mmu.h b/arch/s390/include/asm/mmu.h index bb1b4bef1878..4c2dc7abc285 100644 --- a/arch/s390/include/asm/mmu.h +++ b/arch/s390/include/asm/mmu.h @@ -32,6 +32,11 @@ typedef struct { unsigned int uses_skeys:1; /* The mmu context uses CMM. */ unsigned int uses_cmm:1; + /* + * The mmu context allows COW-sharing of memory pages (KSM, zeropage). + * Note that COW-sharing during fork() is currently always allowed. + */ + unsigned int allow_cow_sharing:1; /* The gmaps associated with this context are allowed to use huge pages. */ unsigned int allow_gmap_hpage_1m:1; } mm_context_t; diff --git a/arch/s390/include/asm/mmu_context.h b/arch/s390/include/asm/mmu_context.h index 929af18b0908..a7789a9f6218 100644 --- a/arch/s390/include/asm/mmu_context.h +++ b/arch/s390/include/asm/mmu_context.h @@ -35,6 +35,7 @@ static inline int init_new_context(struct task_struct *tsk, mm->context.has_pgste = 0; mm->context.uses_skeys = 0; mm->context.uses_cmm = 0; + mm->context.allow_cow_sharing = 1; mm->context.allow_gmap_hpage_1m = 0; #endif switch (mm->context.asce_limit) { diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h index 60950e7a25f5..259c2439c251 100644 --- a/arch/s390/include/asm/pgtable.h +++ b/arch/s390/include/asm/pgtable.h @@ -566,10 +566,20 @@ static inline pud_t set_pud_bit(pud_t pud, pgprot_t prot) } /* - * In the case that a guest uses storage keys - * faults should no longer be backed by zero pages + * As soon as the guest uses storage keys or enables PV, we deduplicate all + * mapped shared zeropages and prevent new shared zeropages from getting + * mapped. */ -#define mm_forbids_zeropage mm_has_pgste +#define mm_forbids_zeropage mm_forbids_zeropage +static inline int mm_forbids_zeropage(struct mm_struct *mm) +{ +#ifdef CONFIG_PGSTE + if (!mm->context.allow_cow_sharing) + return 1; +#endif + return 0; +} + static inline int mm_uses_skeys(struct mm_struct *mm) { #ifdef CONFIG_PGSTE diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index 5147b943a864..db3392f0be21 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -2631,9 +2631,7 @@ static int kvm_s390_handle_pv(struct kvm *kvm, struct kvm_pv_cmd *cmd) if (r) break; - mmap_write_lock(current->mm); - r = gmap_mark_unmergeable(); - mmap_write_unlock(current->mm); + r = s390_disable_cow_sharing(); if (r) break; diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c index 094b43b121cd..9233b0acac89 100644 --- a/arch/s390/mm/gmap.c +++ b/arch/s390/mm/gmap.c @@ -2549,41 +2549,6 @@ static inline void thp_split_mm(struct mm_struct *mm) } #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ -/* - * Remove all empty zero pages from the mapping for lazy refaulting - * - This must be called after mm->context.has_pgste is set, to avoid - * future creation of zero pages - * - This must be called after THP was disabled. - * - * mm contracts with s390, that even if mm were to remove a page table, - * racing with the loop below and so causing pte_offset_map_lock() to fail, - * it will never insert a page table containing empty zero pages once - * mm_forbids_zeropage(mm) i.e. mm->context.has_pgste is set. - */ -static int __zap_zero_pages(pmd_t *pmd, unsigned long start, - unsigned long end, struct mm_walk *walk) -{ - unsigned long addr; - - for (addr = start; addr != end; addr += PAGE_SIZE) { - pte_t *ptep; - spinlock_t *ptl; - - ptep = pte_offset_map_lock(walk->mm, pmd, addr, &ptl); - if (!ptep) - break; - if (is_zero_pfn(pte_pfn(*ptep))) - ptep_xchg_direct(walk->mm, addr, ptep, __pte(_PAGE_INVALID)); - pte_unmap_unlock(ptep, ptl); - } - return 0; -} - -static const struct mm_walk_ops zap_zero_walk_ops = { - .pmd_entry = __zap_zero_pages, - .walk_lock = PGWALK_WRLOCK, -}; - /* * switch on pgstes for its userspace process (for kvm) */ @@ -2601,22 +2566,140 @@ int s390_enable_sie(void) mm->context.has_pgste = 1; /* split thp mappings and disable thp for future mappings */ thp_split_mm(mm); - walk_page_range(mm, 0, TASK_SIZE, &zap_zero_walk_ops, NULL); mmap_write_unlock(mm); return 0; } EXPORT_SYMBOL_GPL(s390_enable_sie); -int gmap_mark_unmergeable(void) +static int find_zeropage_pte_entry(pte_t *pte, unsigned long addr, + unsigned long end, struct mm_walk *walk) +{ + unsigned long *found_addr = walk->private; + + /* Return 1 of the page is a zeropage. */ + if (is_zero_pfn(pte_pfn(*pte))) { + + /* + * Shared zeropage in e.g., a FS DAX mapping? We cannot do the + * right thing and likely don't care: FAULT_FLAG_UNSHARE + * currently only works in COW mappings, which is also where + * mm_forbids_zeropage() is checked. + */ + if (!is_cow_mapping(walk->vma->vm_flags)) + return -EFAULT; + + *found_addr = addr; + return 1; + } + return 0; +} + +static const struct mm_walk_ops find_zeropage_ops = { + .pte_entry = find_zeropage_pte_entry, + .walk_lock = PGWALK_WRLOCK, +}; + +/* + * Unshare all shared zeropages, replacing them by anonymous pages. Note that + * we cannot simply zap all shared zeropages, because this could later + * trigger unexpected userfaultfd missing events. + * + * This must be called after mm->context.allow_cow_sharing was + * set to 0, to avoid future mappings of shared zeropages. + * + * mm contracts with s390, that even if mm were to remove a page table, + * and racing with walk_page_range_vma() calling pte_offset_map_lock() + * would fail, it will never insert a page table containing empty zero + * pages once mm_forbids_zeropage(mm) i.e. + * mm->context.allow_cow_sharing is set to 0. + */ +static int __s390_unshare_zeropages(struct mm_struct *mm) +{ + struct vm_area_struct *vma; + VMA_ITERATOR(vmi, mm, 0); + unsigned long addr; + int rc; + + for_each_vma(vmi, vma) { + /* + * We could only look at COW mappings, but it's more future + * proof to catch unexpected zeropages in other mappings and + * fail. + */ + if ((vma->vm_flags & VM_PFNMAP) || is_vm_hugetlb_page(vma)) + continue; + addr = vma->vm_start; + +retry: + rc = walk_page_range_vma(vma, addr, vma->vm_end, + &find_zeropage_ops, &addr); + if (rc <= 0) + continue; + + /* addr was updated by find_zeropage_pte_entry() */ + rc = handle_mm_fault(vma, addr, + FAULT_FLAG_UNSHARE | FAULT_FLAG_REMOTE, + NULL); + if (rc & VM_FAULT_OOM) + return -ENOMEM; + /* + * See break_ksm(): even after handle_mm_fault() returned 0, we + * must start the lookup from the current address, because + * handle_mm_fault() may back out if there's any difficulty. + * + * VM_FAULT_SIGBUS and VM_FAULT_SIGSEGV are unexpected but + * maybe they could trigger in the future on concurrent + * truncation. In that case, the shared zeropage would be gone + * and we can simply retry and make progress. + */ + cond_resched(); + goto retry; + } + + return rc; +} + +static int __s390_disable_cow_sharing(struct mm_struct *mm) { + int rc; + + if (!mm->context.allow_cow_sharing) + return 0; + + mm->context.allow_cow_sharing = 0; + + /* Replace all shared zeropages by anonymous pages. */ + rc = __s390_unshare_zeropages(mm); /* * Make sure to disable KSM (if enabled for the whole process or * individual VMAs). Note that nothing currently hinders user space * from re-enabling it. */ - return ksm_disable(current->mm); + if (!rc) + rc = ksm_disable(mm); + if (rc) + mm->context.allow_cow_sharing = 1; + return rc; +} + +/* + * Disable most COW-sharing of memory pages for the whole process: + * (1) Disable KSM and unmerge/unshare any KSM pages. + * (2) Disallow shared zeropages and unshare any zerpages that are mapped. + * + * Not that we currently don't bother with COW-shared pages that are shared + * with parent/child processes due to fork(). + */ +int s390_disable_cow_sharing(void) +{ + int rc; + + mmap_write_lock(current->mm); + rc = __s390_disable_cow_sharing(current->mm); + mmap_write_unlock(current->mm); + return rc; } -EXPORT_SYMBOL_GPL(gmap_mark_unmergeable); +EXPORT_SYMBOL_GPL(s390_disable_cow_sharing); /* * Enable storage key handling from now on and initialize the storage @@ -2685,7 +2768,7 @@ int s390_enable_skey(void) goto out_up; mm->context.uses_skeys = 1; - rc = gmap_mark_unmergeable(); + rc = __s390_disable_cow_sharing(mm); if (rc) { mm->context.uses_skeys = 0; goto out_up;

[v3,2/2] s390/mm: re-enable the shared zeropage for !PV and !skeys KVM guests

Commit Message

Comments

Patch