[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [xen master] x86/mm: Add an early PGT_validated exit in _get_page_type()
commit 15d93068e3484cb14006e935734a1e6088f228fd Author: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> AuthorDate: Thu Jun 16 12:08:02 2022 +0100 Commit: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> CommitDate: Wed Jun 22 11:26:36 2022 +0100 x86/mm: Add an early PGT_validated exit in _get_page_type() This is a continuation of the cleanup and commenting in: 9186e96b199e ("x86/pv: Clean up _get_page_type()") 8cc5036bc385 ("x86/pv: Fix ABAC cmpxchg() race in _get_page_type()") With the re-arranged and newly commented logic, it's now obvious that the second half of _get_page_type() only has work to do for page validation. Introduce an early exit for PGT_validated. This makes the fastpath marginally faster, and simplifies the subsequent logic as it no longer needs to exclude the fully validated case. Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx> --- xen/arch/x86/mm.c | 70 +++++++++++++++++++++++++++++++------------------------ 1 file changed, 39 insertions(+), 31 deletions(-) diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c index ac74ae389c..57751d2ed7 100644 --- a/xen/arch/x86/mm.c +++ b/xen/arch/x86/mm.c @@ -3002,6 +3002,17 @@ static int _get_page_type(struct page_info *page, unsigned long type, * fully validated (PGT_[type] | PGT_validated | >0). */ + /* If the page is fully validated, we're done. */ + if ( likely(nx & PGT_validated) ) + return 0; + + /* + * The page is in the "validate locked" state. We have exclusive access, + * and any concurrent callers are waiting in the cmpxchg() loop above. + * + * Exclusive access ends when PGT_validated or PGT_partial get set. + */ + if ( unlikely((x & PGT_count_mask) == 0) ) { struct domain *d = page_get_owner(page); @@ -3071,43 +3082,40 @@ static int _get_page_type(struct page_info *page, unsigned long type, } } - if ( unlikely(!(nx & PGT_validated)) ) + /* + * Flush the cache if there were previously non-coherent mappings of + * this page, and we're trying to use it as anything other than a + * writeable page. This forces the page to be coherent before we + * validate its contents for safety. + */ + if ( (nx & PGT_non_coherent) && type != PGT_writable_page ) { - /* - * Flush the cache if there were previously non-coherent mappings of - * this page, and we're trying to use it as anything other than a - * writeable page. This forces the page to be coherent before we - * validate its contents for safety. - */ - if ( (nx & PGT_non_coherent) && type != PGT_writable_page ) - { - void *addr = __map_domain_page(page); + void *addr = __map_domain_page(page); - cache_flush(addr, PAGE_SIZE); - unmap_domain_page(addr); + cache_flush(addr, PAGE_SIZE); + unmap_domain_page(addr); - page->u.inuse.type_info &= ~PGT_non_coherent; - } + page->u.inuse.type_info &= ~PGT_non_coherent; + } - /* - * No special validation needed for writable or shared pages. Page - * tables and GDT/LDT need to have their contents audited. - * - * per validate_page(), non-atomic updates are fine here. - */ - if ( type == PGT_writable_page || type == PGT_shared_page ) - page->u.inuse.type_info |= PGT_validated; - else + /* + * No special validation needed for writable or shared pages. Page + * tables and GDT/LDT need to have their contents audited. + * + * per validate_page(), non-atomic updates are fine here. + */ + if ( type == PGT_writable_page || type == PGT_shared_page ) + page->u.inuse.type_info |= PGT_validated; + else + { + if ( !(x & PGT_partial) ) { - if ( !(x & PGT_partial) ) - { - page->nr_validated_ptes = 0; - page->partial_flags = 0; - page->linear_pt_count = 0; - } - - rc = validate_page(page, type, preemptible); + page->nr_validated_ptes = 0; + page->partial_flags = 0; + page->linear_pt_count = 0; } + + rc = validate_page(page, type, preemptible); } out: -- generated by git-patchbot for /home/xen/git/xen.git#master
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