Messages in this thread Patch in this message | | | Subject | Re: [PATCH] xen/x86: Adjust stack pointer in xen_sysexit | From | Boris Ostrovsky <> | Date | Tue, 17 Nov 2015 09:40:23 -0500 |
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On 11/16/2015 04:55 PM, H. Peter Anvin wrote: > On 11/16/15 12:22, Borislav Petkov wrote: >> Huh, so what's wrong with a jump: >> >> jmp 1f >> swapgs >> 1: >> > What is the point of that jump? > >>> If it would make you feel better, it could be X86_BUG_XENPV :-p >> That doesn't matter - I just don't want to open the flood gates on >> pseudo feature bits. >> >> hpa, what do you think? > Pseudo feature bits are fine, we already have plenty of them. They make > sense as they let us reuse a lot of infrastructure.
So how about something like this? And then I think we can remove usergs_sysret32 and irq_enable_sysexit pv ops completely as noone will use them (lguest doesn't set them)
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index 3eb572e..c43df7b 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 + /* PV guests always use IRET path */ + ALTERNATIVE "testl %eax, %eax", "jmp .Lsyscall_32_done", X86_FEATURE_PV 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..2d1bc82 100644 --- a/arch/x86/entry/entry_64_compat.S +++ b/arch/x86/entry/entry_64_compat.S @@ -121,7 +121,7 @@ sysenter_flags_fixed:
movq %rsp, %rdi call do_fast_syscall_32 - testl %eax, %eax + ALTERNATIVE "testl %eax, %eax", "jmp .Lsyscall_32_done", X86_FEATURE_PV jz .Lsyscall_32_done jmp sysret32_from_system_call
@@ -200,7 +200,8 @@ ENTRY(entry_SYSCALL_compat)
movq %rsp, %rdi call do_fast_syscall_32 - testl %eax, %eax + /* PV guests always use IRET path */ + ALTERNATIVE "testl %eax, %eax", "jmp .Lsyscall_32_done", X86_FEATURE_PV jz .Lsyscall_32_done
/* Opportunistic SYSRET */ diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h index e4f8010..723327b 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_PV ( 8*32+16) /* Paravirtual guest */
/* Intel-defined CPU features, CPUID level 0x00000007:0 (ebx), word 9 */
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