From 947effc8962261d60ea32e7d1897119c76cf9808 Mon Sep 17 00:00:00 2001 From: Boris Ostrovsky Date: Tue, 17 Nov 2015 15:16:14 -0500 Subject: [PATCH 2/4] x86/xen: Avoid fast syscall path for Xen PV guests After 32-bit syscall rewrite, and specifically after commit 5f310f739b4c ("x86/entry/32: Re-implement SYSENTER using the new C path"), the stack frame that is passed to xen_sysexit is no longer a "standard" one (i.e. it's not pt_regs). Since we end up calling xen_iret from xen_sysexit we don't need to fix up the stack and instead follow entry_SYSENTER_32's IRET path directly to xen_iret. We can do the same thing for compat mode even though stack does not need to be fixed. This will allow us to drop usergs_sysret32 paravirt op (in the subsequent patch) Signed-off-by: Boris Ostrovsky Suggested-by: Andy Lutomirski Signed-off-by: Konrad Rzeszutek Wilk --- arch/x86/entry/entry_32.S | 3 ++- arch/x86/entry/entry_64_compat.S | 6 ++++-- arch/x86/include/asm/cpufeature.h | 1 + arch/x86/xen/enlighten.c | 4 +++- 4 files changed, 10 insertions(+), 4 deletions(-) diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index 3eb572e..901f186 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -308,7 +308,8 @@ sysenter_past_esp: movl %esp, %eax call do_fast_syscall_32 - testl %eax, %eax + /* XEN PV guests always use IRET path */ + ALTERNATIVE "testl %eax, %eax", "xor %eax, %eax", X86_FEATURE_XENPV jz .Lsyscall_32_done /* Opportunistic SYSEXIT */ diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S index c320183..98893d9 100644 --- a/arch/x86/entry/entry_64_compat.S +++ b/arch/x86/entry/entry_64_compat.S @@ -121,7 +121,8 @@ sysenter_flags_fixed: movq %rsp, %rdi call do_fast_syscall_32 - testl %eax, %eax + /* XEN PV guests always use IRET path */ + ALTERNATIVE "testl %eax, %eax", "xor %eax, %eax", X86_FEATURE_XENPV jz .Lsyscall_32_done jmp sysret32_from_system_call @@ -200,7 +201,8 @@ ENTRY(entry_SYSCALL_compat) movq %rsp, %rdi call do_fast_syscall_32 - testl %eax, %eax + /* XEN PV guests always use IRET path */ + ALTERNATIVE "testl %eax, %eax", "xor %eax, %eax", X86_FEATURE_XENPV jz .Lsyscall_32_done /* Opportunistic SYSRET */ diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h index e4f8010..0e4fe5b 100644 --- a/arch/x86/include/asm/cpufeature.h +++ b/arch/x86/include/asm/cpufeature.h @@ -216,6 +216,7 @@ #define X86_FEATURE_PAUSEFILTER ( 8*32+13) /* AMD filtered pause intercept */ #define X86_FEATURE_PFTHRESHOLD ( 8*32+14) /* AMD pause filter threshold */ #define X86_FEATURE_VMMCALL ( 8*32+15) /* Prefer vmmcall to vmcall */ +#define X86_FEATURE_XENPV ( 8*32+16) /* Xen paravirtual guest */ /* Intel-defined CPU features, CPUID level 0x00000007:0 (ebx), word 9 */ diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c index 5774800..d315151 100644 --- a/arch/x86/xen/enlighten.c +++ b/arch/x86/xen/enlighten.c @@ -1886,8 +1886,10 @@ EXPORT_SYMBOL_GPL(xen_hvm_need_lapic); static void xen_set_cpu_features(struct cpuinfo_x86 *c) { - if (xen_pv_domain()) + if (xen_pv_domain()) { clear_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS); + set_cpu_cap(c, X86_FEATURE_XENPV); + } } const struct hypervisor_x86 x86_hyper_xen = { -- 2.5.0