From 2e917175e1ef147a527a9158b9f09773ec94c0bd Mon Sep 17 00:00:00 2001 From: Juergen Gross Date: Fri, 28 Nov 2014 11:53:59 +0100 Subject: [PATCH] xen: Speed up set_phys_to_machine() by using read-only mappings Instead of checking at each call of set_phys_to_machine() whether a new p2m page has to be allocated due to writing an entry in a large invalid or identity area, just map those areas read only and react to a page fault on write by allocating the new page. This change will make the common path with no allocation much faster as it only requires a single write of the new mfn instead of walking the address translation tables and checking for the special cases. Suggested-by: David Vrabel Signed-off-by: Juergen Gross Reviewed-by: David Vrabel Reviewed-by: Konrad Rzeszutek Wilk Signed-off-by: David Vrabel --- arch/x86/xen/p2m.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c index 7d84473..8b5db51b 100644 --- a/arch/x86/xen/p2m.c +++ b/arch/x86/xen/p2m.c @@ -70,6 +70,7 @@ #include #include +#include #include #include @@ -316,9 +317,9 @@ static void __init xen_rebuild_p2m_list(unsigned long *p2m) paravirt_alloc_pte(&init_mm, __pa(p2m_identity_pte) >> PAGE_SHIFT); for (i = 0; i < PTRS_PER_PTE; i++) { set_pte(p2m_missing_pte + i, - pfn_pte(PFN_DOWN(__pa(p2m_missing)), PAGE_KERNEL)); + pfn_pte(PFN_DOWN(__pa(p2m_missing)), PAGE_KERNEL_RO)); set_pte(p2m_identity_pte + i, - pfn_pte(PFN_DOWN(__pa(p2m_identity)), PAGE_KERNEL)); + pfn_pte(PFN_DOWN(__pa(p2m_identity)), PAGE_KERNEL_RO)); } for (pfn = 0; pfn < xen_max_p2m_pfn; pfn += chunk) { @@ -365,7 +366,7 @@ static void __init xen_rebuild_p2m_list(unsigned long *p2m) p2m_missing : p2m_identity; ptep = populate_extra_pte((unsigned long)(p2m + pfn)); set_pte(ptep, - pfn_pte(PFN_DOWN(__pa(mfns)), PAGE_KERNEL)); + pfn_pte(PFN_DOWN(__pa(mfns)), PAGE_KERNEL_RO)); continue; } @@ -624,6 +625,9 @@ bool __set_phys_to_machine(unsigned long pfn, unsigned long mfn) return true; } + if (likely(!__put_user(mfn, xen_p2m_addr + pfn))) + return true; + ptep = lookup_address((unsigned long)(xen_p2m_addr + pfn), &level); BUG_ON(!ptep || level != PG_LEVEL_4K); @@ -633,9 +637,7 @@ bool __set_phys_to_machine(unsigned long pfn, unsigned long mfn) if (pte_pfn(*ptep) == PFN_DOWN(__pa(p2m_identity))) return mfn == IDENTITY_FRAME(pfn); - xen_p2m_addr[pfn] = mfn; - - return true; + return false; } bool set_phys_to_machine(unsigned long pfn, unsigned long mfn) -- 2.7.4