From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:37749 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729045AbgBQKV7 (ORCPT ); Mon, 17 Feb 2020 05:21:59 -0500 Subject: Re: [PATCH v2 05/42] s390/mm: provide memory management functions for protected KVM guests References: <20200214222658.12946-1-borntraeger@de.ibm.com> <20200214222658.12946-6-borntraeger@de.ibm.com> From: David Hildenbrand Message-ID: Date: Mon, 17 Feb 2020 11:21:44 +0100 MIME-Version: 1.0 In-Reply-To: <20200214222658.12946-6-borntraeger@de.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable Sender: linux-s390-owner@vger.kernel.org List-ID: To: Christian Borntraeger , Janosch Frank Cc: KVM , Cornelia Huck , Thomas Huth , Ulrich Weigand , Claudio Imbrenda , linux-s390 , Michael Mueller , Vasily Gorbik , Andrea Arcangeli , linux-mm@kvack.org > diff --git a/arch/s390/include/asm/page.h b/arch/s390/include/asm/page.= h > index 85e944f04c70..4ebcf891ff3c 100644 > --- a/arch/s390/include/asm/page.h > +++ b/arch/s390/include/asm/page.h > @@ -153,6 +153,11 @@ static inline int devmem_is_allowed(unsigned long = pfn) > #define HAVE_ARCH_FREE_PAGE > #define HAVE_ARCH_ALLOC_PAGE > =20 > +#if IS_ENABLED(CONFIG_PGSTE) > +int arch_make_page_accessible(struct page *page); > +#define HAVE_ARCH_MAKE_PAGE_ACCESSIBLE > +#endif > + Feels like this should have been one of the (CONFIG_)ARCH_HAVE_XXX thingies defined via kconfig instead. E.g., like (CONFIG_)HAVE_ARCH_TRANSPARENT_HUGEPAGE [...] > + > +/* > + * Requests the Ultravisor to encrypt a guest page and make it > + * accessible to the host for paging (export). > + * > + * @paddr: Absolute host address of page to be exported > + */ > +int uv_convert_from_secure(unsigned long paddr) > +{ > + struct uv_cb_cfs uvcb =3D { > + .header.cmd =3D UVC_CMD_CONV_FROM_SEC_STOR, > + .header.len =3D sizeof(uvcb), > + .paddr =3D paddr > + }; > + > + if (uv_call(0, (u64)&uvcb)) > + return -EINVAL; > + return 0; > +} > + > +/* > + * Calculate the expected ref_count for a page that would otherwise ha= ve no > + * further pins. This was cribbed from similar functions in other plac= es in > + * the kernel, but with some slight modifications. We know that a secu= re > + * page can not be a huge page for example. s/ca not cannot/ > + */ > +static int expected_page_refs(struct page *page) > +{ > + int res; > + > + res =3D page_mapcount(page); > + if (PageSwapCache(page)) { > + res++; > + } else if (page_mapping(page)) { > + res++; > + if (page_has_private(page)) > + res++; > + } > + return res; > +} > + > +static int make_secure_pte(pte_t *ptep, unsigned long addr, > + struct page *exp_page, struct uv_cb_header *uvcb) > +{ > + pte_t entry =3D READ_ONCE(*ptep); > + struct page *page; > + int expected, rc =3D 0; > + > + if (!pte_present(entry)) > + return -ENXIO; > + if (pte_val(entry) & _PAGE_INVALID) > + return -ENXIO; > + > + page =3D pte_page(entry); > + if (page !=3D exp_page) > + return -ENXIO; > + if (PageWriteback(page)) > + return -EAGAIN; > + expected =3D expected_page_refs(page); > + if (!page_ref_freeze(page, expected)) > + return -EBUSY; > + set_bit(PG_arch_1, &page->flags); > + rc =3D uv_call(0, (u64)uvcb); > + page_ref_unfreeze(page, expected); > + /* Return -ENXIO if the page was not mapped, -EINVAL otherwise */ > + if (rc) > + rc =3D uvcb->rc =3D=3D 0x10a ? -ENXIO : -EINVAL; > + return rc; > +} > + > +/* > + * Requests the Ultravisor to make a page accessible to a guest. > + * If it's brought in the first time, it will be cleared. If > + * it has been exported before, it will be decrypted and integrity > + * checked. > + */ > +int gmap_make_secure(struct gmap *gmap, unsigned long gaddr, void *uvc= b) > +{ > + struct vm_area_struct *vma; > + unsigned long uaddr; > + struct page *page; > + int rc, local_drain =3D 0; local_drain could have been a bool. > + spinlock_t *ptelock; > + pte_t *ptep; > + > +again: > + rc =3D -EFAULT; > + down_read(&gmap->mm->mmap_sem); > + > + uaddr =3D __gmap_translate(gmap, gaddr); > + if (IS_ERR_VALUE(uaddr)) > + goto out; > + vma =3D find_vma(gmap->mm, uaddr); > + if (!vma) > + goto out; > + /* > + * Secure pages cannot be huge and userspace should not combine both. > + * In case userspace does it anyway this will result in an -EFAULT fo= r > + * the unpack. The guest is thus never reaching secure mode. If > + * userspace is playing dirty tricky with mapping huge pages later > + * on this will result in a segmenation fault. s/segmenation/segmentation/ > + */ > + if (is_vm_hugetlb_page(vma)) > + goto out; > + > + rc =3D -ENXIO; > + page =3D follow_page(vma, uaddr, FOLL_WRITE); > + if (IS_ERR_OR_NULL(page)) > + goto out; > + > + lock_page(page); > + ptep =3D get_locked_pte(gmap->mm, uaddr, &ptelock); > + rc =3D make_secure_pte(ptep, uaddr, page, uvcb); > + pte_unmap_unlock(ptep, ptelock); > + unlock_page(page); > +out: > + up_read(&gmap->mm->mmap_sem); > + > + if (rc =3D=3D -EAGAIN) { > + wait_on_page_writeback(page); > + } else if (rc =3D=3D -EBUSY) { > + /* > + * If we have tried a local drain and the page refcount > + * still does not match our expected safe value, try with a > + * system wide drain. This is needed if the pagevecs holding > + * the page are on a different CPU. > + */ > + if (local_drain) { > + lru_add_drain_all(); I do wonder if that is valid to be called with all the locks at this poin= t. > + /* We give up here, and let the caller try again */ > + return -EAGAIN; > + } > + /* > + * We are here if the page refcount does not match the > + * expected safe value. The main culprits are usually > + * pagevecs. With lru_add_drain() we drain the pagevecs > + * on the local CPU so that hopefully the refcount will > + * reach the expected safe value. > + */ > + lru_add_drain(); dito ... > + local_drain =3D 1; > + /* And now we try again immediately after draining */ > + goto again; > + } else if (rc =3D=3D -ENXIO) { > + if (gmap_fault(gmap, gaddr, FAULT_FLAG_WRITE)) > + return -EFAULT; > + return -EAGAIN; > + } > + return rc; > +} > +EXPORT_SYMBOL_GPL(gmap_make_secure); > + > +int gmap_convert_to_secure(struct gmap *gmap, unsigned long gaddr) > +{ > + struct uv_cb_cts uvcb =3D { > + .header.cmd =3D UVC_CMD_CONV_TO_SEC_STOR, > + .header.len =3D sizeof(uvcb), > + .guest_handle =3D gmap->guest_handle, > + .gaddr =3D gaddr, > + }; > + > + return gmap_make_secure(gmap, gaddr, &uvcb); > +} > +EXPORT_SYMBOL_GPL(gmap_convert_to_secure); > + > +/** > + * To be called with the page locked or with an extra reference! Can we have races here? (IOW, two callers concurrently for the same page) > + */ > +int arch_make_page_accessible(struct page *page) > +{ > + int rc =3D 0; > + > + /* Hugepage cannot be protected, so nothing to do */ > + if (PageHuge(page)) > + return 0; > + > + /* > + * PG_arch_1 is used in 3 places: > + * 1. for kernel page tables during early boot > + * 2. for storage keys of huge pages and KVM > + * 3. As an indication that this page might be secure. This can > + * overindicate, e.g. we set the bit before calling > + * convert_to_secure. > + * As secure pages are never huge, all 3 variants can co-exists. > + */ > + if (!test_bit(PG_arch_1, &page->flags)) > + return 0; > + > + rc =3D uv_pin_shared(page_to_phys(page)); > + if (!rc) { > + clear_bit(PG_arch_1, &page->flags); > + return 0; > + } Overall, looks sane to me. (I am mostly concerned about possible races, e.g., when two gmaps would be created for a single VM and nasty stuff be done with them). But yeah, I guess you guys thought about this ;) --=20 Thanks, David / dhildenb