| Message ID | 0290ae707cdd98d57714afb9bc4c3386683c1190.1738933678.git.oleksii.kurochko@gmail.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Fixes for vmap_to_mfn() and pt_mapping_level | expand |
On 07.02.2025 14:13, Oleksii Kurochko wrote: > --- a/xen/arch/riscv/pt.c > +++ b/xen/arch/riscv/pt.c > @@ -238,11 +238,10 @@ pte_t pt_walk(vaddr_t va, unsigned int *pte_level) > > /* Update an entry at the level @target. */ > static int pt_update_entry(mfn_t root, vaddr_t virt, > - mfn_t mfn, unsigned int target, > + mfn_t mfn, unsigned int *target, > unsigned int flags) > { > int rc; > - unsigned int level = HYP_PT_ROOT_LEVEL; > pte_t *table; Considering the lack of an initializer here, ... > @@ -256,39 +255,45 @@ static int pt_update_entry(mfn_t root, vaddr_t virt, > bool alloc_tbl = !mfn_eq(mfn, INVALID_MFN) || (flags & PTE_POPULATE); > pte_t pte, *entry; > > - /* convenience aliases */ > - DECLARE_OFFSETS(offsets, virt); > - > - table = map_table(root); > - for ( ; level > target; level-- ) > + if ( *target == CONFIG_PAGING_LEVELS ) > + entry = _pt_walk(virt, target); > + else > { > - rc = pt_next_level(alloc_tbl, &table, offsets[level]); > - if ( rc == XEN_TABLE_MAP_NOMEM ) > + unsigned int level = HYP_PT_ROOT_LEVEL; > + /* convenience aliases */ > + DECLARE_OFFSETS(offsets, virt); > + > + table = map_table(root); > + for ( ; level > *target; level-- ) > { > - rc = -ENOMEM; > - goto out; > + rc = pt_next_level(alloc_tbl, &table, offsets[level]); > + if ( rc == XEN_TABLE_MAP_NOMEM ) > + { > + rc = -ENOMEM; > + goto out; > + } > + > + if ( rc == XEN_TABLE_MAP_NONE ) > + { > + rc = 0; > + goto out; > + } > + > + if ( rc != XEN_TABLE_NORMAL ) > + break; > } > > - if ( rc == XEN_TABLE_MAP_NONE ) > + if ( level != *target ) > { > - rc = 0; > + dprintk(XENLOG_ERR, > + "%s: Shattering superpage is not supported\n", __func__); > + rc = -EOPNOTSUPP; > goto out; > } > > - if ( rc != XEN_TABLE_NORMAL ) > - break; > - } > - > - if ( level != target ) > - { > - dprintk(XENLOG_ERR, > - "%s: Shattering superpage is not supported\n", __func__); > - rc = -EOPNOTSUPP; > - goto out; > + entry = table + offsets[level]; > } > > - entry = table + offsets[level]; > - > rc = -EINVAL; > if ( !pt_check_entry(*entry, mfn, flags) ) > goto out; ... I'm surprised the compiler doesn't complain about use of a possibly uninitialized variable at out: unmap_table(table); For the new path you're adding the variable is uninitialized afaict. Which implies that you're again failing to unmap what _pt_walk() has handed you. Jan
On 2/10/25 5:53 PM, Jan Beulich wrote: > On 07.02.2025 14:13, Oleksii Kurochko wrote: >> --- a/xen/arch/riscv/pt.c >> +++ b/xen/arch/riscv/pt.c >> @@ -238,11 +238,10 @@ pte_t pt_walk(vaddr_t va, unsigned int *pte_level) >> >> /* Update an entry at the level @target. */ >> static int pt_update_entry(mfn_t root, vaddr_t virt, >> - mfn_t mfn, unsigned int target, >> + mfn_t mfn, unsigned int *target, >> unsigned int flags) >> { >> int rc; >> - unsigned int level = HYP_PT_ROOT_LEVEL; >> pte_t *table; > Considering the lack of an initializer here, ... > >> @@ -256,39 +255,45 @@ static int pt_update_entry(mfn_t root, vaddr_t virt, >> bool alloc_tbl = !mfn_eq(mfn, INVALID_MFN) || (flags & PTE_POPULATE); >> pte_t pte, *entry; >> >> - /* convenience aliases */ >> - DECLARE_OFFSETS(offsets, virt); >> - >> - table = map_table(root); >> - for ( ; level > target; level-- ) >> + if ( *target == CONFIG_PAGING_LEVELS ) >> + entry = _pt_walk(virt, target); >> + else >> { >> - rc = pt_next_level(alloc_tbl, &table, offsets[level]); >> - if ( rc == XEN_TABLE_MAP_NOMEM ) >> + unsigned int level = HYP_PT_ROOT_LEVEL; >> + /* convenience aliases */ >> + DECLARE_OFFSETS(offsets, virt); >> + >> + table = map_table(root); >> + for ( ; level > *target; level-- ) >> { >> - rc = -ENOMEM; >> - goto out; >> + rc = pt_next_level(alloc_tbl, &table, offsets[level]); >> + if ( rc == XEN_TABLE_MAP_NOMEM ) >> + { >> + rc = -ENOMEM; >> + goto out; >> + } >> + >> + if ( rc == XEN_TABLE_MAP_NONE ) >> + { >> + rc = 0; >> + goto out; >> + } >> + >> + if ( rc != XEN_TABLE_NORMAL ) >> + break; >> } >> >> - if ( rc == XEN_TABLE_MAP_NONE ) >> + if ( level != *target ) >> { >> - rc = 0; >> + dprintk(XENLOG_ERR, >> + "%s: Shattering superpage is not supported\n", __func__); >> + rc = -EOPNOTSUPP; >> goto out; >> } >> >> - if ( rc != XEN_TABLE_NORMAL ) >> - break; >> - } >> - >> - if ( level != target ) >> - { >> - dprintk(XENLOG_ERR, >> - "%s: Shattering superpage is not supported\n", __func__); >> - rc = -EOPNOTSUPP; >> - goto out; >> + entry = table + offsets[level]; >> } >> >> - entry = table + offsets[level]; >> - >> rc = -EINVAL; >> if ( !pt_check_entry(*entry, mfn, flags) ) >> goto out; > ... I'm surprised the compiler doesn't complain about use of a possibly > uninitialized variable at > > out: > unmap_table(table); > > For the new path you're adding the variable is uninitialized afaict. > Which implies that you're again failing to unmap what _pt_walk() has > handed you. Thanks, unmapping of table and entry (in the case of the new patch) should be really updated. I'll take care of it in the next patch version. ~ Oleksii
diff --git a/xen/arch/riscv/pt.c b/xen/arch/riscv/pt.c index 66cb976b55..8c15a48f60 100644 --- a/xen/arch/riscv/pt.c +++ b/xen/arch/riscv/pt.c @@ -238,11 +238,10 @@ pte_t pt_walk(vaddr_t va, unsigned int *pte_level) /* Update an entry at the level @target. */ static int pt_update_entry(mfn_t root, vaddr_t virt, - mfn_t mfn, unsigned int target, + mfn_t mfn, unsigned int *target, unsigned int flags) { int rc; - unsigned int level = HYP_PT_ROOT_LEVEL; pte_t *table; /* * The intermediate page table shouldn't be allocated when MFN isn't @@ -256,39 +255,45 @@ static int pt_update_entry(mfn_t root, vaddr_t virt, bool alloc_tbl = !mfn_eq(mfn, INVALID_MFN) || (flags & PTE_POPULATE); pte_t pte, *entry; - /* convenience aliases */ - DECLARE_OFFSETS(offsets, virt); - - table = map_table(root); - for ( ; level > target; level-- ) + if ( *target == CONFIG_PAGING_LEVELS ) + entry = _pt_walk(virt, target); + else { - rc = pt_next_level(alloc_tbl, &table, offsets[level]); - if ( rc == XEN_TABLE_MAP_NOMEM ) + unsigned int level = HYP_PT_ROOT_LEVEL; + /* convenience aliases */ + DECLARE_OFFSETS(offsets, virt); + + table = map_table(root); + for ( ; level > *target; level-- ) { - rc = -ENOMEM; - goto out; + rc = pt_next_level(alloc_tbl, &table, offsets[level]); + if ( rc == XEN_TABLE_MAP_NOMEM ) + { + rc = -ENOMEM; + goto out; + } + + if ( rc == XEN_TABLE_MAP_NONE ) + { + rc = 0; + goto out; + } + + if ( rc != XEN_TABLE_NORMAL ) + break; } - if ( rc == XEN_TABLE_MAP_NONE ) + if ( level != *target ) { - rc = 0; + dprintk(XENLOG_ERR, + "%s: Shattering superpage is not supported\n", __func__); + rc = -EOPNOTSUPP; goto out; } - if ( rc != XEN_TABLE_NORMAL ) - break; - } - - if ( level != target ) - { - dprintk(XENLOG_ERR, - "%s: Shattering superpage is not supported\n", __func__); - rc = -EOPNOTSUPP; - goto out; + entry = table + offsets[level]; } - entry = table + offsets[level]; - rc = -EINVAL; if ( !pt_check_entry(*entry, mfn, flags) ) goto out; @@ -413,17 +418,40 @@ static int pt_update(vaddr_t virt, mfn_t mfn, while ( left ) { - unsigned int order, level; - - level = pt_mapping_level(vfn, mfn, left, flags); - order = XEN_PT_LEVEL_ORDER(level); + unsigned int order, level = CONFIG_PAGING_LEVELS; - ASSERT(left >= BIT(order, UL)); + /* + * In the case when modifying or destroying a mapping, it is necessary + * to search until a leaf node is found, instead of searching for + * a page table entry based on the precalculated `level` and `order` + * (look at pt_update()). + * This is because when `mfn` == INVALID_MFN, the `mask`(in + * pt_mapping_level()) will take into account only `vfn`, which could + * accidentally return an incorrect level, leading to the discovery of + * an incorrect page table entry. + * + * For example, if `vfn` is page table level 1 aligned, but it was + * mapped as page table level 0, then pt_mapping_level() will return + * `level` = 1, since only `vfn` (which is page table level 1 aligned) + * is taken into account when `mfn` == INVALID_MFN + * (look at pt_mapping_level()). + * + * To force searching until a leaf node is found is necessary to have + * `level` == CONFIG_PAGING_LEVELS which is a default value for + * `level`. + * + * For other cases (when a mapping is not being modified or destroyed), + * pt_mapping_level() should be used. + */ + if ( !mfn_eq(mfn, INVALID_MFN) || (flags & PTE_POPULATE) ) + level = pt_mapping_level(vfn, mfn, left, flags); - rc = pt_update_entry(root, vfn << PAGE_SHIFT, mfn, level, flags); + rc = pt_update_entry(root, vfn << PAGE_SHIFT, mfn, &level, flags); if ( rc ) break; + order = XEN_PT_LEVEL_ORDER(level); + vfn += 1UL << order; if ( !mfn_eq(mfn, INVALID_MFN) ) mfn = mfn_add(mfn, 1UL << order);
When pt_update() is called with arguments (..., INVALID_MFN, ..., 0 or 1), it indicates that a mapping is being destroyed/modifyed. In the case when modifying or destroying a mapping, it is necessary to search until a leaf node is found, instead of searching for a page table entry based on the precalculated `level` and `order`(look at pt_update()). This is because when `mfn` == INVALID_MFN, the `mask` (in pt_mapping_level()) will take into account only `vfn`, which could accidentally return an incorrect level, leading to the discovery of an incorrect page table entry. For example, if `vfn` is page table level 1 aligned, but it was mapped as page table level 0, then pt_mapping_level() will return `level` = 1, since only `vfn` (which is page table level 1 aligned) is taken into account when `mfn` == INVALID_MFN (look at pt_mapping_level()). Fixes: c2f1ded524 ("xen/riscv: page table handling") Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com> --- Changes in v3: - Drop ASSERT() for order as it isn't needed anymore. - Drop PTE_LEAF_SEARCH and use instead level=CONFIG_PAGING_LEVELS; refactor connected code correspondingly. - Calculate order once. - Drop initializer for local variable order. - Drop BUG_ON(!pte_is_mapping(*entry)) for the case when leaf searching happens as there is a similar check in pt_check_entry(). Look at pt.c:41 and pt.c:75. --- Changes in v2: - Introduce PTE_LEAF_SEARCH to tell page table update operation to walk down to wherever the leaf entry is. - Use introduced PTE_LEAF_SEARCH to not searching pte_t entry twice. - Update the commit message. --- xen/arch/riscv/pt.c | 90 +++++++++++++++++++++++++++++---------------- 1 file changed, 59 insertions(+), 31 deletions(-)