[patch 10/10] x86/mm/cpa: Avoid the 4k pages check completely
The extra loop which tries hard to preserve large pages in case of conflicts with static protection regions turns out to be not preserving anything, at least not in the experiments which have been conducted. There might be corner cases in which the code would be able to preserve a large page oaccsionally, but it's really not worth the extra code and the cycles wasted in the common case. Before: 1G pages checked:2 1G pages sameprot: 0 1G pages preserved: 0 2M pages checked: 541 2M pages sameprot: 466 2M pages preserved: 47 4K pages checked: 514 4K pages set-checked: 7668 After: 1G pages checked:2 1G pages sameprot: 0 1G pages preserved: 0 2M pages checked: 538 2M pages sameprot: 466 2M pages preserved: 47 4K pages set-checked: 7668 Signed-off-by: Thomas Gleixner --- arch/x86/mm/pageattr.c | 66 - 1 file changed, 17 insertions(+), 49 deletions(-) --- a/arch/x86/mm/pageattr.c +++ b/arch/x86/mm/pageattr.c @@ -111,7 +111,6 @@ static unsigned long cpa_1g_preserved; static unsigned long cpa_2m_checked; static unsigned long cpa_2m_sameprot; static unsigned long cpa_2m_preserved; -static unsigned long cpa_4k_checked; static unsigned long cpa_4k_install; static inline void cpa_inc_1g_checked(void) @@ -124,11 +123,6 @@ static inline void cpa_inc_2m_checked(vo cpa_2m_checked++; } -static inline void cpa_inc_4k_checked(void) -{ - cpa_4k_checked++; -} - static inline void cpa_inc_4k_install(void) { cpa_4k_install++; @@ -158,7 +152,6 @@ static int cpastats_show(struct seq_file seq_printf(m, "2M pages checked: %16lu\n", cpa_2m_checked); seq_printf(m, "2M pages sameprot:%16lu\n", cpa_2m_sameprot); seq_printf(m, "2M pages preserved: %16lu\n", cpa_2m_preserved); - seq_printf(m, "4K pages checked: %16lu\n", cpa_4k_checked); seq_printf(m, "4K pages set-checked: %16lu\n", cpa_4k_install); return 0; } @@ -185,7 +178,6 @@ late_initcall(cpa_stats_init); #else static inline void cpa_inc_1g_checked(void) { } static inline void cpa_inc_2m_checked(void) { } -static inline void cpa_inc_4k_checked(void) { } static inline void cpa_inc_4k_install(void) { } static inline void cpa_inc_lp_sameprot(int level) { } static inline void cpa_inc_lp_preserved(int level) { } @@ -741,11 +733,10 @@ static pgprot_t pgprot_clear_protnone_bi static int __should_split_large_page(pte_t *kpte, unsigned long address, struct cpa_data *cpa) { - unsigned long numpages, pmask, psize, lpaddr, addr, pfn, old_pfn; + unsigned long numpages, pmask, psize, lpaddr, pfn, old_pfn; pgprot_t old_prot, new_prot, req_prot, chk_prot; pte_t new_pte, old_pte, *tmp; enum pg_level level; - int i; /* * Check for races, another CPU might have split this page @@ -850,53 +841,30 @@ static int __should_split_large_page(pte } /* -* Optimization: Check whether the requested pgprot is conflicting -* with a static protection requirement in the large page. If not, -* then checking whether the requested range is fully covering the -* large page can be done right here. +* If the requested range does not cover the full page, split it up */ - new_prot = static_protections(req_prot, lpaddr, old_pfn, numpages, - CPA_DETECT); - - if (pgprot_val(req_prot) == pgprot_val(new_prot)) { - if (address != lpaddr || cpa->numpages != numpages) - return 1; - goto setlp; - } + if (address != lpaddr || cpa->numpages != numpages) + return 1; /* -* Slow path. The full large page check above established that the -* requested pgprot cannot be applied to the full large page due to -* conflicting requirements of static protection regions. It might -* turn out that the whole requested range is covered by the -* modified protection of the first 4k segment at @address. This -* might result in the ability to preserve the large page -* nevertheless. -*/ - new_prot = static_protections(req_prot, address, pfn, 1, CPA_DETECT); - pfn = old_pfn; - for (i = 0, addr = lpaddr; i < numpages; i++, addr += PAGE_SIZE, pfn++) { - chk_prot = static_protections(req_prot, addr, pfn, 1, - CPA_DETECT); - cpa_inc_4k_checked(); - if (pgprot_val(chk_prot) != pgprot_val(new_prot)) - return 1; - } - - /* If there are no changes,
[patch 10/10] x86/mm/cpa: Avoid the 4k pages check completely
The extra loop which tries hard to preserve large pages in case of conflicts with static protection regions turns out to be not preserving anything, at least not in the experiments which have been conducted. There might be corner cases in which the code would be able to preserve a large page oaccsionally, but it's really not worth the extra code and the cycles wasted in the common case. Before: 1G pages checked:2 1G pages sameprot: 0 1G pages preserved: 0 2M pages checked: 541 2M pages sameprot: 466 2M pages preserved: 47 4K pages checked: 514 4K pages set-checked: 7668 After: 1G pages checked:2 1G pages sameprot: 0 1G pages preserved: 0 2M pages checked: 538 2M pages sameprot: 466 2M pages preserved: 47 4K pages set-checked: 7668 Signed-off-by: Thomas Gleixner --- arch/x86/mm/pageattr.c | 66 - 1 file changed, 17 insertions(+), 49 deletions(-) --- a/arch/x86/mm/pageattr.c +++ b/arch/x86/mm/pageattr.c @@ -111,7 +111,6 @@ static unsigned long cpa_1g_preserved; static unsigned long cpa_2m_checked; static unsigned long cpa_2m_sameprot; static unsigned long cpa_2m_preserved; -static unsigned long cpa_4k_checked; static unsigned long cpa_4k_install; static inline void cpa_inc_1g_checked(void) @@ -124,11 +123,6 @@ static inline void cpa_inc_2m_checked(vo cpa_2m_checked++; } -static inline void cpa_inc_4k_checked(void) -{ - cpa_4k_checked++; -} - static inline void cpa_inc_4k_install(void) { cpa_4k_install++; @@ -158,7 +152,6 @@ static int cpastats_show(struct seq_file seq_printf(m, "2M pages checked: %16lu\n", cpa_2m_checked); seq_printf(m, "2M pages sameprot:%16lu\n", cpa_2m_sameprot); seq_printf(m, "2M pages preserved: %16lu\n", cpa_2m_preserved); - seq_printf(m, "4K pages checked: %16lu\n", cpa_4k_checked); seq_printf(m, "4K pages set-checked: %16lu\n", cpa_4k_install); return 0; } @@ -185,7 +178,6 @@ late_initcall(cpa_stats_init); #else static inline void cpa_inc_1g_checked(void) { } static inline void cpa_inc_2m_checked(void) { } -static inline void cpa_inc_4k_checked(void) { } static inline void cpa_inc_4k_install(void) { } static inline void cpa_inc_lp_sameprot(int level) { } static inline void cpa_inc_lp_preserved(int level) { } @@ -741,11 +733,10 @@ static pgprot_t pgprot_clear_protnone_bi static int __should_split_large_page(pte_t *kpte, unsigned long address, struct cpa_data *cpa) { - unsigned long numpages, pmask, psize, lpaddr, addr, pfn, old_pfn; + unsigned long numpages, pmask, psize, lpaddr, pfn, old_pfn; pgprot_t old_prot, new_prot, req_prot, chk_prot; pte_t new_pte, old_pte, *tmp; enum pg_level level; - int i; /* * Check for races, another CPU might have split this page @@ -850,53 +841,30 @@ static int __should_split_large_page(pte } /* -* Optimization: Check whether the requested pgprot is conflicting -* with a static protection requirement in the large page. If not, -* then checking whether the requested range is fully covering the -* large page can be done right here. +* If the requested range does not cover the full page, split it up */ - new_prot = static_protections(req_prot, lpaddr, old_pfn, numpages, - CPA_DETECT); - - if (pgprot_val(req_prot) == pgprot_val(new_prot)) { - if (address != lpaddr || cpa->numpages != numpages) - return 1; - goto setlp; - } + if (address != lpaddr || cpa->numpages != numpages) + return 1; /* -* Slow path. The full large page check above established that the -* requested pgprot cannot be applied to the full large page due to -* conflicting requirements of static protection regions. It might -* turn out that the whole requested range is covered by the -* modified protection of the first 4k segment at @address. This -* might result in the ability to preserve the large page -* nevertheless. -*/ - new_prot = static_protections(req_prot, address, pfn, 1, CPA_DETECT); - pfn = old_pfn; - for (i = 0, addr = lpaddr; i < numpages; i++, addr += PAGE_SIZE, pfn++) { - chk_prot = static_protections(req_prot, addr, pfn, 1, - CPA_DETECT); - cpa_inc_4k_checked(); - if (pgprot_val(chk_prot) != pgprot_val(new_prot)) - return 1; - } - - /* If there are no changes,