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Peter Anvin" CC: , , , , , Elliot Berman X-Mailer: b4 0.14.1 X-ClientProxiedBy: nalasex01a.na.qualcomm.com (10.47.209.196) To nasanex01b.na.qualcomm.com (10.46.141.250) X-QCInternal: smtphost X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=5800 signatures=585085 X-Proofpoint-ORIG-GUID: VKocc11VXrfwDcfhSZyfG1SnIgFpRfUU X-Proofpoint-GUID: VKocc11VXrfwDcfhSZyfG1SnIgFpRfUU X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1039,Hydra:6.0.680,FMLib:17.12.28.16 definitions=2024-08-29_06,2024-08-29_02,2024-05-17_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 mlxlogscore=721 priorityscore=1501 bulkscore=0 impostorscore=0 adultscore=0 malwarescore=0 phishscore=0 lowpriorityscore=0 mlxscore=0 spamscore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2407110000 definitions=main-2408290158 When memory is made inaccessible to the host, Linux may still speculatively access the folio if a load_unaligned_zeropad is performed at the end of the prior page. To ensure Linux itself catches such errors without hypervisor crashing Linux, unmap the guest-inaccessible pages from the direct map. This feature is made optional because arm64 pKVM can provide a special, detectable fault which can be fixed up directly. Signed-off-by: Elliot Berman --- include/linux/guest_memfd.h | 1 + mm/guest_memfd.c | 79 +++++++++++++++++++++++++++++++++++++++++++-- 2 files changed, 78 insertions(+), 2 deletions(-) diff --git a/include/linux/guest_memfd.h b/include/linux/guest_memfd.h index 66e5d3ab42613..de53bce15db99 100644 --- a/include/linux/guest_memfd.h +++ b/include/linux/guest_memfd.h @@ -33,6 +33,7 @@ enum guest_memfd_grab_flags { enum guest_memfd_create_flags { GUEST_MEMFD_FLAG_CLEAR_INACCESSIBLE = (1UL << 0), + GUEST_MEMFD_FLAG_REMOVE_DIRECT_MAP = (1UL << 1), }; struct folio *guest_memfd_grab_folio(struct file *file, pgoff_t index, u32 flags); diff --git a/mm/guest_memfd.c b/mm/guest_memfd.c index 194b2c3ea1525..d4232739d4c5b 100644 --- a/mm/guest_memfd.c +++ b/mm/guest_memfd.c @@ -8,6 +8,7 @@ #include #include #include +#include #include #include "internal.h" @@ -26,6 +27,45 @@ struct guest_memfd_private { atomic_t safe; }; +static inline int folio_set_direct_map_invalid_noflush(struct folio *folio) +{ + unsigned long i, nr = folio_nr_pages(folio); + int r; + + for (i = 0; i < nr; i++) { + struct page *page = folio_page(folio, i); + + r = set_direct_map_invalid_noflush(page); + if (r) + goto out_remap; + } + /** + * Currently no need to flush as hypervisor will also be flushing + * tlb when giving the folio to guest. + */ + + return 0; +out_remap: + for (; i > 0; i--) { + struct page *page = folio_page(folio, i - 1); + + BUG_ON(set_direct_map_default_noflush(page)); + } + + return r; +} + +static inline void folio_set_direct_map_default_noflush(struct folio *folio) +{ + unsigned long i, nr = folio_nr_pages(folio); + + for (i = 0; i < nr; i++) { + struct page *page = folio_page(folio, i); + + BUG_ON(set_direct_map_default_noflush(page)); + } +} + static inline int base_safe_refs(struct folio *folio) { /* 1 for filemap */ @@ -131,6 +171,12 @@ struct folio *guest_memfd_grab_folio(struct file *file, pgoff_t index, u32 flags goto out_free; } } else { + if (gmem_flags & GUEST_MEMFD_FLAG_REMOVE_DIRECT_MAP) { + r = folio_set_direct_map_invalid_noflush(folio); + if (r < 0) + goto out_free; + } + if (ops->prepare_inaccessible) { r = ops->prepare_inaccessible(inode, folio); if (r < 0) @@ -203,6 +249,7 @@ int guest_memfd_make_accessible(struct folio *folio) struct guest_memfd_private *private = folio_get_private(folio); struct inode *inode = folio_inode(folio); struct guest_memfd_operations *ops = inode->i_private; + unsigned long gmem_flags; int r; /* @@ -218,6 +265,10 @@ int guest_memfd_make_accessible(struct folio *folio) if (!r) return -EBUSY; + gmem_flags = (unsigned long)inode->i_mapping->i_private_data; + if (gmem_flags & GUEST_MEMFD_FLAG_REMOVE_DIRECT_MAP) + folio_set_direct_map_default_noflush(folio); + if (ops->prepare_accessible) { r = ops->prepare_accessible(inode, folio); if (r) @@ -248,6 +299,7 @@ int guest_memfd_make_inaccessible(struct folio *folio) struct guest_memfd_private *private = folio_get_private(folio); struct inode *inode = folio_inode(folio); struct guest_memfd_operations *ops = inode->i_private; + unsigned long gmem_flags; int r; r = atomic_dec_if_positive(&private->accessible); @@ -266,6 +318,13 @@ int guest_memfd_make_inaccessible(struct folio *folio) goto err; } + gmem_flags = (unsigned long)inode->i_mapping->i_private_data; + if (gmem_flags & GUEST_MEMFD_FLAG_REMOVE_DIRECT_MAP) { + r = folio_set_direct_map_invalid_noflush(folio); + if (r) + goto err; + } + if (ops->prepare_inaccessible) { r = ops->prepare_inaccessible(inode, folio); if (r) @@ -454,6 +513,7 @@ static int gmem_error_folio(struct address_space *mapping, struct folio *folio) struct guest_memfd_operations *ops = inode->i_private; off_t offset = folio->index; size_t nr = folio_nr_pages(folio); + unsigned long gmem_flags; int ret; filemap_invalidate_lock_shared(mapping); @@ -464,6 +524,10 @@ static int gmem_error_folio(struct address_space *mapping, struct folio *folio) filemap_invalidate_unlock_shared(mapping); + gmem_flags = (unsigned long)inode->i_mapping->i_private_data; + if (gmem_flags & GUEST_MEMFD_FLAG_REMOVE_DIRECT_MAP) + folio_set_direct_map_default_noflush(folio); + return ret; } @@ -474,7 +538,7 @@ static bool gmem_release_folio(struct folio *folio, gfp_t gfp) struct guest_memfd_operations *ops = inode->i_private; off_t offset = folio->index; size_t nr = folio_nr_pages(folio); - unsigned long val, expected; + unsigned long val, expected, gmem_flags; int ret; ret = ops->invalidate_begin(inode, offset, nr); @@ -483,6 +547,10 @@ static bool gmem_release_folio(struct folio *folio, gfp_t gfp) if (ops->invalidate_end) ops->invalidate_end(inode, offset, nr); + gmem_flags = (unsigned long)inode->i_mapping->i_private_data; + if (gmem_flags & GUEST_MEMFD_FLAG_REMOVE_DIRECT_MAP) + folio_set_direct_map_default_noflush(folio); + expected = base_safe_refs(folio); val = atomic_read(&private->safe); WARN_ONCE(val != expected, "folio[%x] safe ref: %d != expected %d\n", @@ -518,7 +586,14 @@ static inline bool guest_memfd_check_ops(const struct guest_memfd_operations *op static inline unsigned long guest_memfd_valid_flags(void) { - return GUEST_MEMFD_FLAG_CLEAR_INACCESSIBLE; + unsigned long flags = GUEST_MEMFD_FLAG_CLEAR_INACCESSIBLE; + +#ifdef CONFIG_ARCH_HAS_SET_DIRECT_MAP + if (can_set_direct_map()) + flags |= GUEST_MEMFD_FLAG_REMOVE_DIRECT_MAP; +#endif + + return flags; } /**