[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [xen staging] xen/arm: mm: Avoid flushing the TLBs when mapping are inserted
commit 07d11f63d03ee919038e707e6618846cf4e6df0f Author: Julien Grall <jgrall@xxxxxxxxxx> AuthorDate: Fri May 20 13:09:24 2022 +0100 Commit: Julien Grall <jgrall@xxxxxxxxxx> CommitDate: Wed Jun 8 11:04:53 2022 +0100 xen/arm: mm: Avoid flushing the TLBs when mapping are inserted Currently, the function xen_pt_update() will flush the TLBs even when the mappings are inserted. This is a bit wasteful because we don't allow mapping replacement. Even if we were, the flush would need to happen earlier because mapping replacement should use Break-Before-Make when updating the entry. A single call to xen_pt_update() can perform a single action. IOW, it is not possible to, for instance, mix inserting and removing mappings. Therefore, we can use `flags` to determine what action is performed. This change will be particularly help to limit the impact of switching boot time mapping to use xen_pt_update(). Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx> Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx> Reviewed-by: Luca Fancellu <luca.fancellu@xxxxxxx> Tested-by: Luca Fancellu <luca.fancellu@xxxxxxx> --- xen/arch/arm/mm.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-) diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c index c4487dd7fc..747083d820 100644 --- a/xen/arch/arm/mm.c +++ b/xen/arch/arm/mm.c @@ -1119,7 +1119,13 @@ static bool xen_pt_check_entry(lpae_t entry, mfn_t mfn, unsigned int level, /* We should be here with a valid MFN. */ ASSERT(!mfn_eq(mfn, INVALID_MFN)); - /* We don't allow replacing any valid entry. */ + /* + * We don't allow replacing any valid entry. + * + * Note that the function xen_pt_update() relies on this + * assumption and will skip the TLB flush. The function will need + * to be updated if the check is relaxed. + */ if ( lpae_is_valid(entry) ) { if ( lpae_is_mapping(entry, level) ) @@ -1434,11 +1440,16 @@ static int xen_pt_update(unsigned long virt, } /* - * Flush the TLBs even in case of failure because we may have + * The TLBs flush can be safely skipped when a mapping is inserted + * as we don't allow mapping replacement (see xen_pt_check_entry()). + * + * For all the other cases, the TLBs will be flushed unconditionally + * even if the mapping has failed. This is because we may have * partially modified the PT. This will prevent any unexpected * behavior afterwards. */ - flush_xen_tlb_range_va(virt, PAGE_SIZE * nr_mfns); + if ( !((flags & _PAGE_PRESENT) && !mfn_eq(mfn, INVALID_MFN)) ) + flush_xen_tlb_range_va(virt, PAGE_SIZE * nr_mfns); spin_unlock(&xen_pt_lock); -- generated by git-patchbot for /home/xen/git/xen.git#staging
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