From: Julien Grall Date: Fri, 20 May 2016 13:37:42 +0000 (+0100) Subject: xen/arm: p2m: Release the p2m lock before undoing the mappings X-Git-Tag: archive/raspbian/4.8.0-1+rpi1~1^2~1101 X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=ed2cddb66b40cacdefd2e7920bde578d8da67fa9;p=xen.git xen/arm: p2m: Release the p2m lock before undoing the mappings Since commit 4b25423a "arch/arm: unmap partially-mapped memory regions", Xen has been undoing the P2M mappings when an error occurred during insertion or memory allocation. This is done by calling recursively apply_p2m_changes, however the second call is done with the p2m lock taken which will result in a deadlock for the current processor. The p2m lock is here to protect 2 threads modifying concurrently the page tables. However, it does not guarantee the ordering of the changes. I.e if 2 threads request change on regions that overlaps, then the result is undefined. Therefore it is fine to move the recursive call to undo the changes after the lock is released. Signed-off-by: Julien Grall Reviewed-by: Wei Chen Reviewed-by: Stefano Stabellini Tested-by: Wei Chen --- diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c index 68c67b01d1..838d004fb5 100644 --- a/xen/arch/arm/p2m.c +++ b/xen/arch/arm/p2m.c @@ -1184,6 +1184,14 @@ out: while ( (pg = page_list_remove_head(&free_pages)) ) free_domheap_page(pg); + for ( level = P2M_ROOT_LEVEL; level < 4; level ++ ) + { + if ( mappings[level] ) + unmap_domain_page(mappings[level]); + } + + spin_unlock(&p2m->lock); + if ( rc < 0 && ( op == INSERT || op == ALLOCATE ) && addr != start_gpaddr ) { @@ -1196,14 +1204,6 @@ out: mattr, 0, p2m_invalid, d->arch.p2m.default_access); } - for ( level = P2M_ROOT_LEVEL; level < 4; level ++ ) - { - if ( mappings[level] ) - unmap_domain_page(mappings[level]); - } - - spin_unlock(&p2m->lock); - return rc; }