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d="scan'208";a="16168815" From: Andrew Cooper To: Xen-devel Subject: [PATCH 3/3] x86/pv: Compile out compat_gdt in !CONFIG_PV builds Date: Fri, 17 Apr 2020 16:50:04 +0100 Message-ID: <20200417155004.16806-4-andrew.cooper3@citrix.com> X-Mailer: git-send-email 2.11.0 In-Reply-To: <20200417155004.16806-1-andrew.cooper3@citrix.com> References: <20200417155004.16806-1-andrew.cooper3@citrix.com> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Andrew Cooper , Wei Liu , Jan Beulich , =?UTF-8?q?Roger=20Pau=20Monn=C3=A9?= Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" There is no need for the Compat GDT if there are no 32bit PV guests. This saves 4k per online CPU Bloat-o-meter reports the following savings in Xen itself: add/remove: 0/3 grow/shrink: 1/4 up/down: 7/-4612 (-4605) Function old new delta cpu_smpboot_free 1249 1256 +7 per_cpu__compat_gdt_l1e 8 - -8 per_cpu__compat_gdt 8 - -8 init_idt_traps 442 420 -22 load_system_tables 414 364 -50 trap_init 444 280 -164 cpu_smpboot_callback 1255 991 -264 boot_compat_gdt 4096 - -4096 Total: Before=3062726, After=3058121, chg -0.15% Signed-off-by: Andrew Cooper --- CC: Jan Beulich CC: Wei Liu CC: Roger Pau Monné The increase in cpu_smpboot_free() appears to be a consequence of a totally different layout of basic blocks. --- xen/arch/x86/cpu/common.c | 5 +++-- xen/arch/x86/desc.c | 2 ++ xen/arch/x86/smpboot.c | 5 ++++- xen/arch/x86/traps.c | 10 +++++++--- 4 files changed, 16 insertions(+), 6 deletions(-) diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c index 1b33f1ed71..7b093cb421 100644 --- a/xen/arch/x86/cpu/common.c +++ b/xen/arch/x86/cpu/common.c @@ -752,8 +752,9 @@ void load_system_tables(void) _set_tssldt_desc(gdt + TSS_ENTRY, (unsigned long)tss, sizeof(*tss) - 1, SYS_DESC_tss_avail); - _set_tssldt_desc(compat_gdt + TSS_ENTRY, (unsigned long)tss, - sizeof(*tss) - 1, SYS_DESC_tss_busy); + if ( IS_ENABLED(CONFIG_PV32) ) + _set_tssldt_desc(compat_gdt + TSS_ENTRY, (unsigned long)tss, + sizeof(*tss) - 1, SYS_DESC_tss_busy); per_cpu(full_gdt_loaded, cpu) = false; lgdt(&gdtr); diff --git a/xen/arch/x86/desc.c b/xen/arch/x86/desc.c index dfeb1beaa8..39080ca672 100644 --- a/xen/arch/x86/desc.c +++ b/xen/arch/x86/desc.c @@ -55,6 +55,7 @@ seg_desc_t boot_gdt[PAGE_SIZE / sizeof(seg_desc_t)] = [SEL2GDT(PER_CPU_SELECTOR)] = { 0x0000910000000000 }, }; +#ifdef CONFIG_PV32 __section(".data.page_aligned") __aligned(PAGE_SIZE) seg_desc_t boot_compat_gdt[PAGE_SIZE / sizeof(seg_desc_t)] = { @@ -83,6 +84,7 @@ seg_desc_t boot_compat_gdt[PAGE_SIZE / sizeof(seg_desc_t)] = /* 0xe060 - per-CPU entry (limit == cpu) */ [SEL2GDT(PER_CPU_SELECTOR)] = { 0x0000910000000000 }, }; +#endif /* * Used by each CPU as it starts up, to enter C with a suitable %cs. diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c index 09264b02d1..f9f63e496f 100644 --- a/xen/arch/x86/smpboot.c +++ b/xen/arch/x86/smpboot.c @@ -959,7 +959,8 @@ static void cpu_smpboot_free(unsigned int cpu, bool remove) free_domheap_page(mfn_to_page(mfn)); } - FREE_XENHEAP_PAGE(per_cpu(compat_gdt, cpu)); + if ( IS_ENABLED(CONFIG_PV32) ) + FREE_XENHEAP_PAGE(per_cpu(compat_gdt, cpu)); if ( remove ) { @@ -1001,6 +1002,7 @@ static int cpu_smpboot_alloc(unsigned int cpu) BUILD_BUG_ON(NR_CPUS > 0x10000); gdt[PER_CPU_GDT_ENTRY - FIRST_RESERVED_GDT_ENTRY].a = cpu; +#ifdef CONFIG_PV32 per_cpu(compat_gdt, cpu) = gdt = alloc_xenheap_pages(0, memflags); if ( gdt == NULL ) goto out; @@ -1008,6 +1010,7 @@ static int cpu_smpboot_alloc(unsigned int cpu) l1e_from_pfn(virt_to_mfn(gdt), __PAGE_HYPERVISOR_RW); memcpy(gdt, boot_compat_gdt, NR_RESERVED_GDT_PAGES * PAGE_SIZE); gdt[PER_CPU_GDT_ENTRY - FIRST_RESERVED_GDT_ENTRY].a = cpu; +#endif if ( idt_tables[cpu] == NULL ) idt_tables[cpu] = alloc_xenheap_pages(0, memflags); diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c index e838846c6b..0bcf554e93 100644 --- a/xen/arch/x86/traps.c +++ b/xen/arch/x86/traps.c @@ -100,8 +100,10 @@ static DEFINE_PER_CPU(unsigned long, last_extable_addr); DEFINE_PER_CPU_READ_MOSTLY(seg_desc_t *, gdt); DEFINE_PER_CPU_READ_MOSTLY(l1_pgentry_t, gdt_l1e); +#ifdef CONFIG_PV32 DEFINE_PER_CPU_READ_MOSTLY(seg_desc_t *, compat_gdt); DEFINE_PER_CPU_READ_MOSTLY(l1_pgentry_t, compat_gdt_l1e); +#endif /* Master table, used by CPU0. */ idt_entry_t __section(".bss.page_aligned") __aligned(PAGE_SIZE) @@ -1999,7 +2001,8 @@ void __init init_idt_traps(void) idt_tables[0] = idt_table; this_cpu(gdt) = boot_gdt; - this_cpu(compat_gdt) = boot_compat_gdt; + if ( IS_ENABLED(CONFIG_PV32) ) + this_cpu(compat_gdt) = boot_compat_gdt; } extern void (*const autogen_entrypoints[X86_NR_VECTORS])(void); @@ -2030,8 +2033,9 @@ void __init trap_init(void) /* Cache {,compat_}gdt_l1e now that physically relocation is done. */ this_cpu(gdt_l1e) = l1e_from_pfn(virt_to_mfn(boot_gdt), __PAGE_HYPERVISOR_RW); - this_cpu(compat_gdt_l1e) = - l1e_from_pfn(virt_to_mfn(boot_compat_gdt), __PAGE_HYPERVISOR_RW); + if ( IS_ENABLED(CONFIG_PV32) ) + this_cpu(compat_gdt_l1e) = + l1e_from_pfn(virt_to_mfn(boot_compat_gdt), __PAGE_HYPERVISOR_RW); percpu_traps_init(); -- 2.11.0