Date: Sun, 17 Sep 2023 10:37:23 GMT From: Mark Johnston <markj@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: aa3bcaad5107 - main - amd64: Add a leaf PTP when pmap_enter(psind=1) creates a wired mapping Message-ID: <202309171037.38HAbNtH023783@gitrepo.freebsd.org>
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The branch main has been updated by markj: URL: https://cgit.FreeBSD.org/src/commit/?id=aa3bcaad51076ceb346fa0c64ab69a35e5241b20 commit aa3bcaad51076ceb346fa0c64ab69a35e5241b20 Author: Bojan Novković <bojan.novkovic@fer.hr> AuthorDate: 2023-09-15 10:41:10 +0000 Commit: Mark Johnston <markj@FreeBSD.org> CommitDate: 2023-09-17 10:27:22 +0000 amd64: Add a leaf PTP when pmap_enter(psind=1) creates a wired mapping This patch reverts the changes made in D19670 and fixes the original issue by allocating and prepopulating a leaf page table page for wired userspace 2M pages. The original issue is an edge case that creates an unmapped, wired region in userspace. Subsequent faults on this region can trigger wired superpage creation, which leads to a panic in pmap_demote_pde_locked() as the pmap does not create a leaf page table page for the wired superpage. D19670 fixed this by disallowing preemptive creation of wired superpage mappings, but that fix is currently interfering with an ongoing effort of speeding up vm_map_wire for large, contiguous entries (e.g. bhyve wiring guest memory). Reviewed by: alc, markj Sponsored by: Google, Inc. (GSoC 2023) MFC after: 2 weeks Differential Revision: https://reviews.freebsd.org/D41132 --- sys/amd64/amd64/pmap.c | 27 +++++++++++++++++++++++++-- 1 file changed, 25 insertions(+), 2 deletions(-) diff --git a/sys/amd64/amd64/pmap.c b/sys/amd64/amd64/pmap.c index b10997fd657b..ff83d8749313 100644 --- a/sys/amd64/amd64/pmap.c +++ b/sys/amd64/amd64/pmap.c @@ -7493,9 +7493,8 @@ pmap_enter_pde(pmap_t pmap, vm_offset_t va, pd_entry_t newpde, u_int flags, pd_entry_t oldpde, *pde; pt_entry_t PG_G, PG_RW, PG_V; vm_page_t mt, pdpg; + vm_page_t uwptpg; - KASSERT(pmap == kernel_pmap || (newpde & PG_W) == 0, - ("pmap_enter_pde: cannot create wired user mapping")); PG_G = pmap_global_bit(pmap); PG_RW = pmap_rw_bit(pmap); KASSERT((newpde & (pmap_modified_bit(pmap) | PG_RW)) != PG_RW, @@ -7592,6 +7591,22 @@ pmap_enter_pde(pmap_t pmap, vm_offset_t va, pd_entry_t newpde, u_int flags, } } + /* + * Allocate leaf ptpage for wired userspace pages. + */ + uwptpg = NULL; + if ((newpde & PG_W) != 0 && pmap != kernel_pmap) { + uwptpg = pmap_alloc_pt_page(pmap, pmap_pde_pindex(va), + VM_ALLOC_WIRED); + if (uwptpg == NULL) + return (KERN_RESOURCE_SHORTAGE); + if (pmap_insert_pt_page(pmap, uwptpg, true, false)) { + pmap_free_pt_page(pmap, uwptpg, false); + return (KERN_RESOURCE_SHORTAGE); + } + + uwptpg->ref_count = NPTEPG; + } if ((newpde & PG_MANAGED) != 0) { /* * Abort this mapping if its PV entry could not be created. @@ -7599,6 +7614,14 @@ pmap_enter_pde(pmap_t pmap, vm_offset_t va, pd_entry_t newpde, u_int flags, if (!pmap_pv_insert_pde(pmap, va, newpde, flags, lockp)) { if (pdpg != NULL) pmap_abort_ptp(pmap, va, pdpg); + if (uwptpg != NULL) { + mt = pmap_remove_pt_page(pmap, va); + KASSERT(mt == uwptpg, + ("removed pt page %p, expected %p", mt, + uwptpg)); + uwptpg->ref_count = 1; + pmap_free_pt_page(pmap, uwptpg, false); + } CTR2(KTR_PMAP, "pmap_enter_pde: failure for va %#lx" " in pmap %p", va, pmap); return (KERN_RESOURCE_SHORTAGE);
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