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Mon, 21 Sep 2026 04:14:24 -0700 (PDT) From: SeungJu Cheon To: Anup Patel Cc: Atish Patra , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Paolo Bonzini , Andrew Jones , Jinyu Tang , Wang Yechao , kvm-riscv@lists.infradead.org, kvm@vger.kernel.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, SeungJu Cheon Subject: [PATCH v1 2/5] KVM: riscv: Read G-stage PTEs once when walking page tables Date: Mon, 21 Sep 2026 20:13:59 +0900 Message-ID: <20260921111402.120911-3-suunj1331@gmail.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260921111402.120911-1-suunj1331@gmail.com> References: <20260921111402.120911-1-suunj1331@gmail.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit gstage_pte_leaf() dereferences the PTE pointer, causing walkers to read the same entry multiple times. This is safe under mmu_lock, but a lockless walker could observe different values when deciding whether an entry is a leaf and which child table to follow. Make gstage_pte_leaf() take a PTE value and use a single snapshot for presence, leaf and child-table checks. Also remove a redundant leaf check in kvm_riscv_gstage_set_pte(), where mmu_lock prevents the entry from changing. Signed-off-by: SeungJu Cheon --- arch/riscv/kvm/gstage.c | 48 +++++++++++++++++++++++------------------ 1 file changed, 27 insertions(+), 21 deletions(-) diff --git a/arch/riscv/kvm/gstage.c b/arch/riscv/kvm/gstage.c index f61ba434093c..944fa4c95aea 100644 --- a/arch/riscv/kvm/gstage.c +++ b/arch/riscv/kvm/gstage.c @@ -19,8 +19,8 @@ unsigned long kvm_riscv_gstage_max_pgd_levels __ro_after_init = 3; unsigned long kvm_riscv_gstage_max_pgd_levels __ro_after_init = 2; #endif -#define gstage_pte_leaf(__ptep) \ - (pte_val(*(__ptep)) & (_PAGE_READ | _PAGE_WRITE | _PAGE_EXEC)) +#define gstage_pte_leaf(__pte) \ + (pte_val(__pte) & (_PAGE_READ | _PAGE_WRITE | _PAGE_EXEC)) static inline unsigned long gstage_pte_index(struct kvm_gstage *gstage, gpa_t addr, u32 level) @@ -84,14 +84,18 @@ static int gstage_level_to_page_size(struct kvm_gstage *gstage, u32 level, bool kvm_riscv_gstage_get_leaf(struct kvm_gstage *gstage, gpa_t addr, pte_t **ptepp, u32 *ptep_level) { - pte_t *ptep; + pte_t *ptep, pte; u32 current_level = gstage->pgd_levels - 1; *ptep_level = current_level; ptep = (pte_t *)gstage->pgd; ptep = &ptep[gstage_pte_index(gstage, addr, current_level)]; - while (ptep && pte_val(ptep_get(ptep))) { - if (gstage_pte_leaf(ptep)) { + while (ptep) { + pte = ptep_get(ptep); + if (!pte_val(pte)) + break; + + if (gstage_pte_leaf(pte)) { *ptep_level = current_level; *ptepp = ptep; return true; @@ -100,7 +104,7 @@ bool kvm_riscv_gstage_get_leaf(struct kvm_gstage *gstage, gpa_t addr, if (current_level) { current_level--; *ptep_level = current_level; - ptep = (pte_t *)gstage_pte_page_vaddr(ptep_get(ptep)); + ptep = (pte_t *)gstage_pte_page_vaddr(pte); ptep = &ptep[gstage_pte_index(gstage, addr, current_level)]; } else { ptep = NULL; @@ -151,10 +155,12 @@ int kvm_riscv_gstage_set_pte(struct kvm_gstage *gstage, return -EINVAL; while (current_level != map->level) { - if (gstage_pte_leaf(ptep)) + pte_t pte = ptep_get(ptep); + + if (gstage_pte_leaf(pte)) return -EEXIST; - if (!pte_val(ptep_get(ptep))) { + if (!pte_val(pte)) { if (!pcache) return -ENOMEM; next_ptep = kvm_mmu_memory_cache_alloc(pcache); @@ -163,9 +169,7 @@ int kvm_riscv_gstage_set_pte(struct kvm_gstage *gstage, set_pte(ptep, pfn_pte(PFN_DOWN(__pa(next_ptep)), __pgprot(_PAGE_TABLE))); } else { - if (gstage_pte_leaf(ptep)) - return -EEXIST; - next_ptep = (pte_t *)gstage_pte_page_vaddr(ptep_get(ptep)); + next_ptep = (pte_t *)gstage_pte_page_vaddr(pte); } current_level--; @@ -175,7 +179,7 @@ int kvm_riscv_gstage_set_pte(struct kvm_gstage *gstage, if (pte_val(*ptep) != pte_val(map->pte)) { bool was_invalid = !pte_val(*ptep); set_pte(ptep, map->pte); - if (gstage_pte_leaf(ptep) && + if (gstage_pte_leaf(map->pte) && !(was_invalid && riscv_has_extension_unlikely(RISCV_ISA_EXT_SVVPTC))) gstage_tlb_flush(gstage, current_level, map->addr); } @@ -316,7 +320,7 @@ bool kvm_riscv_gstage_split_huge(struct kvm_gstage *gstage, unsigned long huge_pte, child_pte; unsigned long child_page_size; bool need_flush = false; - pte_t *ptep; + pte_t *ptep, pte; int i, ret; if (!pcache) @@ -325,16 +329,17 @@ bool kvm_riscv_gstage_split_huge(struct kvm_gstage *gstage, while(current_level > target_level) { ptep = (pte_t *)&next_ptep[gstage_pte_index(gstage, addr, current_level)]; - if (!pte_val(ptep_get(ptep))) + pte = ptep_get(ptep); + if (!pte_val(pte)) break; - if (!gstage_pte_leaf(ptep)) { - next_ptep = (pte_t *)gstage_pte_page_vaddr(ptep_get(ptep)); + if (!gstage_pte_leaf(pte)) { + next_ptep = (pte_t *)gstage_pte_page_vaddr(pte); current_level--; continue; } - huge_pte = pte_val(ptep_get(ptep)); + huge_pte = pte_val(pte); ret = gstage_level_to_page_size(gstage, current_level - 1, &child_page_size); if (ret) @@ -373,7 +378,7 @@ bool kvm_riscv_gstage_op_pte(struct kvm_gstage *gstage, gpa_t addr, pte_t *ptep, u32 ptep_level, enum kvm_riscv_gstage_op op) { int i, ret; - pte_t old_pte, *next_ptep; + pte_t old_pte, pte, *next_ptep; u32 next_ptep_level; unsigned long next_page_size, page_size; bool flush = false; @@ -384,11 +389,12 @@ bool kvm_riscv_gstage_op_pte(struct kvm_gstage *gstage, gpa_t addr, WARN_ON(addr & (page_size - 1)); - if (!pte_val(ptep_get(ptep))) + pte = ptep_get(ptep); + if (!pte_val(pte)) return false; - if (ptep_level && !gstage_pte_leaf(ptep)) { - next_ptep = (pte_t *)gstage_pte_page_vaddr(ptep_get(ptep)); + if (ptep_level && !gstage_pte_leaf(pte)) { + next_ptep = (pte_t *)gstage_pte_page_vaddr(pte); next_ptep_level = ptep_level - 1; ret = gstage_level_to_page_size(gstage, next_ptep_level, &next_page_size); if (ret) -- 2.52.0