diff options
| -rw-r--r-- | arch/x86/xen/p2m.c | 36 |
1 files changed, 36 insertions, 0 deletions
diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c index ffd08c4..64effdc6 100644 --- a/arch/x86/xen/p2m.c +++ b/arch/x86/xen/p2m.c @@ -706,6 +706,7 @@ int m2p_add_override(unsigned long mfn, struct page *page, unsigned long uninitialized_var(address); unsigned level; pte_t *ptep = NULL; + int ret = 0; pfn = page_to_pfn(page); if (!PageHighMem(page)) { @@ -741,6 +742,24 @@ int m2p_add_override(unsigned long mfn, struct page *page, list_add(&page->lru, &m2p_overrides[mfn_hash(mfn)]); spin_unlock_irqrestore(&m2p_override_lock, flags); + /* p2m(m2p(mfn)) == mfn: the mfn is already present somewhere in + * this domain. Set the FOREIGN_FRAME_BIT in the p2m for the other + * pfn so that the following mfn_to_pfn(mfn) calls will return the + * pfn from the m2p_override (the backend pfn) instead. + * We need to do this because the pages shared by the frontend + * (xen-blkfront) can be already locked (lock_page, called by + * do_read_cache_page); when the userspace backend tries to use them + * with direct_IO, mfn_to_pfn returns the pfn of the frontend, so + * do_blockdev_direct_IO is going to try to lock the same pages + * again resulting in a deadlock. + * As a side effect get_user_pages_fast might not be safe on the + * frontend pages while they are being shared with the backend, + * because mfn_to_pfn (that ends up being called by GUPF) will + * return the backend pfn rather than the frontend pfn. */ + ret = __get_user(pfn, &machine_to_phys_mapping[mfn]); + if (ret == 0 && get_phys_to_machine(pfn) == mfn) + set_phys_to_machine(pfn, FOREIGN_FRAME(mfn)); + return 0; } EXPORT_SYMBOL_GPL(m2p_add_override); @@ -752,6 +771,7 @@ int m2p_remove_override(struct page *page, bool clear_pte) unsigned long uninitialized_var(address); unsigned level; pte_t *ptep = NULL; + int ret = 0; pfn = page_to_pfn(page); mfn = get_phys_to_machine(pfn); @@ -821,6 +841,22 @@ int m2p_remove_override(struct page *page, bool clear_pte) } else set_phys_to_machine(pfn, page->index); + /* p2m(m2p(mfn)) == FOREIGN_FRAME(mfn): the mfn is already present + * somewhere in this domain, even before being added to the + * m2p_override (see comment above in m2p_add_override). + * If there are no other entries in the m2p_override corresponding + * to this mfn, then remove the FOREIGN_FRAME_BIT from the p2m for + * the original pfn (the one shared by the frontend): the backend + * cannot do any IO on this page anymore because it has been + * unshared. Removing the FOREIGN_FRAME_BIT from the p2m entry of + * the original pfn causes mfn_to_pfn(mfn) to return the frontend + * pfn again. */ + mfn &= ~FOREIGN_FRAME_BIT; + ret = __get_user(pfn, &machine_to_phys_mapping[mfn]); + if (ret == 0 && get_phys_to_machine(pfn) == FOREIGN_FRAME(mfn) && + m2p_find_override(mfn) == NULL) + set_phys_to_machine(pfn, mfn); + return 0; } EXPORT_SYMBOL_GPL(m2p_remove_override); |
