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SUSE:SLE-12-SP1:GA
xen.10697
5c7e70c6-x86-mm-L2-unvalidation-preemptible.patch
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File 5c7e70c6-x86-mm-L2-unvalidation-preemptible.patch of Package xen.10697
# Commit 176ebf9c8bc2828f6637eb61cc1cf166e302c699 # Date 2019-03-05 13:51:18 +0100 # Author Jan Beulich <jbeulich@suse.com> # Committer Jan Beulich <jbeulich@suse.com> x86/mm: also allow L2 (un)validation to be fully preemptible Commit c612481d1c ("x86/mm: Plumbing to allow any PTE update to fail with -ERESTART") added assertions next to the {alloc,free}_l2_table() invocations to document (and validate in debug builds) that L2 (un)validations are always preemptible. The assertion in free_page_type() was now observed to trigger when recursive L2 page tables get cleaned up. In particular put_page_from_l2e()'s assumption that _put_page_type() would always succeed is now wrong, resulting in a partially un-validated page left in a domain, which has no other means of getting cleaned up later on. If not causing any problems earlier, this would ultimately trigger the check for ->u.inuse.type_info having a zero count when freeing the page during cleanup after the domain has died. As a result it should be considered a mistake to not have extended preemption fully to L2 when it was added to L3/L4 table handling, which this change aims to correct. The validation side additions are done just for symmetry. This is part of XSA-290. Reported-by: Manuel Bouyer <bouyer@antioche.eu.org> Tested-by: Manuel Bouyer <bouyer@antioche.eu.org> Signed-off-by: Jan Beulich <jbeulich@suse.com> Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com> --- a/xen/arch/x86/mm.c +++ b/xen/arch/x86/mm.c @@ -1104,7 +1104,7 @@ get_page_from_l1e( define_get_linear_pagetable(l2); static int get_page_from_l2e( - l2_pgentry_t l2e, unsigned long pfn, struct domain *d) + l2_pgentry_t l2e, unsigned long pfn, struct domain *d, int partial) { unsigned long mfn = l2e_get_pfn(l2e); int rc; @@ -1120,7 +1120,8 @@ get_page_from_l2e( if ( !(l2e_get_flags(l2e) & _PAGE_PSE) ) { - rc = get_page_and_type_from_pagenr(mfn, PGT_l1_page_table, d, 0, 0); + rc = get_page_and_type_from_pagenr(mfn, PGT_l1_page_table, d, + partial, 0); if ( unlikely(rc == -EINVAL) && get_l2_linear_pagetable(l2e, pfn, d) ) rc = 0; return rc; @@ -1324,8 +1325,11 @@ void put_page_from_l1e(l1_pgentry_t l1e, * NB. Virtual address 'l2e' maps to a machine address within frame 'pfn'. * Note also that this automatically deals correctly with linear p.t.'s. */ -static int put_page_from_l2e(l2_pgentry_t l2e, unsigned long pfn) +static int put_page_from_l2e(l2_pgentry_t l2e, unsigned long pfn, + int partial, bool_t defer) { + int rc = 0; + if ( !(l2e_get_flags(l2e) & _PAGE_PRESENT) || (l2e_get_pfn(l2e) == pfn) ) return 1; @@ -1334,13 +1338,27 @@ static int put_page_from_l2e(l2_pgentry_ else { struct page_info *pg = l2e_get_page(l2e); - int rc = _put_page_type(pg, 0, mfn_to_page(pfn)); + struct page_info *ptpg = mfn_to_page(pfn); - ASSERT(!rc); - put_page(pg); + if ( unlikely(partial > 0) ) + { + ASSERT(!defer); + rc = _put_page_type(pg, 1, ptpg); + } + else if ( defer ) + { + current->arch.old_guest_ptpg = ptpg; + current->arch.old_guest_table = pg; + } + else + { + rc = _put_page_type(pg, 1, ptpg); + if ( likely(!rc) ) + put_page(pg); + } } - return 0; + return rc; } static int put_page_from_l3e(l3_pgentry_t l3e, unsigned long pfn, @@ -1515,11 +1533,12 @@ static int alloc_l2_table(struct page_in unsigned long pfn = page_to_mfn(page); l2_pgentry_t *pl2e; unsigned int i; - int rc = 0; + int rc = 0, partial = page->partial_pte; pl2e = map_domain_page(pfn); - for ( i = page->nr_validated_ptes; i < L2_PAGETABLE_ENTRIES; i++ ) + for ( i = page->nr_validated_ptes; i < L2_PAGETABLE_ENTRIES; + i++, partial = 0 ) { if ( i > page->nr_validated_ptes && hypercall_preempt_check() ) { @@ -1529,23 +1548,33 @@ static int alloc_l2_table(struct page_in } if ( !is_guest_l2_slot(d, type, i) || - (rc = get_page_from_l2e(pl2e[i], pfn, d)) > 0 ) + (rc = get_page_from_l2e(pl2e[i], pfn, d, partial)) > 0 ) continue; - if ( unlikely(rc == -EAGAIN) ) + if ( rc == -EAGAIN ) { page->nr_validated_ptes = i; - break; + page->partial_pte = partial ?: 1; } - - if ( rc < 0 ) + else if ( rc == -EINTR && i ) + { + page->nr_validated_ptes = i; + page->partial_pte = 0; + rc = -EAGAIN; + } + else if ( rc < 0 && rc != -EINTR ) { MEM_LOG("Failure in alloc_l2_table: entry %d", i); - while ( i-- > 0 ) - if ( is_guest_l2_slot(d, type, i) ) - put_page_from_l2e(pl2e[i], pfn); - break; + if ( i ) + { + page->nr_validated_ptes = i; + page->partial_pte = 0; + current->arch.old_guest_ptpg = NULL; + current->arch.old_guest_table = page; + } } + if ( rc < 0 ) + break; adjust_guest_l2e(pl2e[i], d); } @@ -1735,28 +1764,50 @@ static int free_l2_table(struct page_inf struct domain *d = page_get_owner(page); unsigned long pfn = page_to_mfn(page); l2_pgentry_t *pl2e; - unsigned int i = page->nr_validated_ptes - 1; - int err = 0; + int rc = 0, partial = page->partial_pte; + unsigned int i = page->nr_validated_ptes - !partial; pl2e = map_domain_page(pfn); - ASSERT(page->nr_validated_ptes); - do { - if ( is_guest_l2_slot(d, page->u.inuse.type_info, i) && - put_page_from_l2e(pl2e[i], pfn) == 0 && - i && hypercall_preempt_check() ) + for ( ; ; ) + { + if ( is_guest_l2_slot(d, page->u.inuse.type_info, i) ) + rc = put_page_from_l2e(pl2e[i], pfn, partial, 0); + if ( rc < 0 ) + break; + + partial = 0; + + if ( !i-- ) + break; + + if ( hypercall_preempt_check() ) { - page->nr_validated_ptes = i; - err = -EAGAIN; + rc = -EINTR; + break; } - } while ( !err && i-- ); + } unmap_domain_page(pl2e); - if ( !err ) + if ( rc >= 0 ) + { page->u.inuse.type_info &= ~PGT_pae_xen_l2; + rc = 0; + } + else if ( rc == -EAGAIN ) + { + page->nr_validated_ptes = i; + page->partial_pte = partial ?: -1; + } + else if ( rc == -EINTR && i < L2_PAGETABLE_ENTRIES - 1 ) + { + page->nr_validated_ptes = i + 1; + page->partial_pte = 0; + rc = -EAGAIN; + } - return err; + return rc; } static int free_l3_table(struct page_info *page) @@ -2056,7 +2107,7 @@ static int mod_l2_entry(l2_pgentry_t *pl return -EBUSY; } - if ( unlikely((rc = get_page_from_l2e(nl2e, pfn, d)) < 0) ) + if ( unlikely((rc = get_page_from_l2e(nl2e, pfn, d, 0)) < 0) ) return rc; adjust_guest_l2e(nl2e, d); @@ -2075,7 +2126,8 @@ static int mod_l2_entry(l2_pgentry_t *pl return -EBUSY; } - put_page_from_l2e(ol2e, pfn); + put_page_from_l2e(ol2e, pfn, 0, 1); + return rc; }
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