Would like to absolutely minimize changes at this point. On July 28, 2014 8:39:43 PM PDT, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: >On Mon, Jul 28, 2014 at 3:33 PM, tip-bot for Andy Lutomirski ><tipbot@xxxxxxxxx> wrote: >> Commit-ID: 7209a75d2009dbf7745e2fd354abf25c3deb3ca3 >> Gitweb: >http://git.kernel.org/tip/7209a75d2009dbf7745e2fd354abf25c3deb3ca3 >> Author: Andy Lutomirski <luto@xxxxxxxxxxxxxx> >> AuthorDate: Wed, 23 Jul 2014 08:34:11 -0700 >> Committer: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx> >> CommitDate: Mon, 28 Jul 2014 15:25:40 -0700 >> >> x86_64/entry/xen: Do not invoke espfix64 on Xen >> >> This moves the espfix64 logic into native_iret. To make this work, >> it gets rid of the native patch for INTERRUPT_RETURN: >> INTERRUPT_RETURN on native kernels is now 'jmp native_iret'. >> >> This changes the 16-bit SS behavior on Xen from OOPSing to leaking >> some bits of the Xen hypervisor's RSP (I think). >> >> [ hpa: this is a nonzero cost on native, but probably not enough to >> measure. Xen needs to fix this in their own code, probably doing >> something equivalent to espfix64. ] > >Any plan to either fix or remove the buggy bsp-only initialization of >espfix64 on paravirt? It's harmless now, but IMO it's still ugly. Or >should this wait for 3.17? > >--Andy > >> >> Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx> >> Link: >http://lkml.kernel.org/r/7b8f1d8ef6597cb16ae004a43c56980a7de3cf94.1406129132.git.luto@xxxxxxxxxxxxxx >> Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx> >> Cc: <stable@xxxxxxxxxxxxxxx> >> --- >> arch/x86/include/asm/irqflags.h | 2 +- >> arch/x86/kernel/entry_64.S | 28 >++++++++++------------------ >> arch/x86/kernel/paravirt_patch_64.c | 2 -- >> 3 files changed, 11 insertions(+), 21 deletions(-) >> >> diff --git a/arch/x86/include/asm/irqflags.h >b/arch/x86/include/asm/irqflags.h >> index bba3cf8..0a8b519 100644 >> --- a/arch/x86/include/asm/irqflags.h >> +++ b/arch/x86/include/asm/irqflags.h >> @@ -129,7 +129,7 @@ static inline notrace unsigned long >arch_local_irq_save(void) >> >> #define PARAVIRT_ADJUST_EXCEPTION_FRAME /* */ >> >> -#define INTERRUPT_RETURN iretq >> +#define INTERRUPT_RETURN jmp native_iret >> #define USERGS_SYSRET64 \ >> swapgs; \ >> sysretq; >> diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S >> index b25ca96..c844f08 100644 >> --- a/arch/x86/kernel/entry_64.S >> +++ b/arch/x86/kernel/entry_64.S >> @@ -830,27 +830,24 @@ restore_args: >> RESTORE_ARGS 1,8,1 >> >> irq_return: >> + INTERRUPT_RETURN >> + >> +ENTRY(native_iret) >> /* >> * Are we returning to a stack segment from the LDT? Note: >in >> * 64-bit mode SS:RSP on the exception stack is always valid. >> */ >> #ifdef CONFIG_X86_ESPFIX64 >> testb $4,(SS-RIP)(%rsp) >> - jnz irq_return_ldt >> + jnz native_irq_return_ldt >> #endif >> >> -irq_return_iret: >> - INTERRUPT_RETURN >> - _ASM_EXTABLE(irq_return_iret, bad_iret) >> - >> -#ifdef CONFIG_PARAVIRT >> -ENTRY(native_iret) >> +native_irq_return_iret: >> iretq >> - _ASM_EXTABLE(native_iret, bad_iret) >> -#endif >> + _ASM_EXTABLE(native_irq_return_iret, bad_iret) >> >> #ifdef CONFIG_X86_ESPFIX64 >> -irq_return_ldt: >> +native_irq_return_ldt: >> pushq_cfi %rax >> pushq_cfi %rdi >> SWAPGS >> @@ -872,7 +869,7 @@ irq_return_ldt: >> SWAPGS >> movq %rax,%rsp >> popq_cfi %rax >> - jmp irq_return_iret >> + jmp native_irq_return_iret >> #endif >> >> .section .fixup,"ax" >> @@ -956,13 +953,8 @@ __do_double_fault: >> cmpl $__KERNEL_CS,CS(%rdi) >> jne do_double_fault >> movq RIP(%rdi),%rax >> - cmpq $irq_return_iret,%rax >> -#ifdef CONFIG_PARAVIRT >> - je 1f >> - cmpq $native_iret,%rax >> -#endif >> + cmpq $native_irq_return_iret,%rax >> jne do_double_fault /* This shouldn't happen... >*/ >> -1: >> movq PER_CPU_VAR(kernel_stack),%rax >> subq $(6*8-KERNEL_STACK_OFFSET),%rax /* Reset to original >stack */ >> movq %rax,RSP(%rdi) >> @@ -1428,7 +1420,7 @@ error_sti: >> */ >> error_kernelspace: >> incl %ebx >> - leaq irq_return_iret(%rip),%rcx >> + leaq native_irq_return_iret(%rip),%rcx >> cmpq %rcx,RIP+8(%rsp) >> je error_swapgs >> movl %ecx,%eax /* zero extend */ >> diff --git a/arch/x86/kernel/paravirt_patch_64.c >b/arch/x86/kernel/paravirt_patch_64.c >> index 3f08f34..a1da673 100644 >> --- a/arch/x86/kernel/paravirt_patch_64.c >> +++ b/arch/x86/kernel/paravirt_patch_64.c >> @@ -6,7 +6,6 @@ DEF_NATIVE(pv_irq_ops, irq_disable, "cli"); >> DEF_NATIVE(pv_irq_ops, irq_enable, "sti"); >> DEF_NATIVE(pv_irq_ops, restore_fl, "pushq %rdi; popfq"); >> DEF_NATIVE(pv_irq_ops, save_fl, "pushfq; popq %rax"); >> -DEF_NATIVE(pv_cpu_ops, iret, "iretq"); >> DEF_NATIVE(pv_mmu_ops, read_cr2, "movq %cr2, %rax"); >> DEF_NATIVE(pv_mmu_ops, read_cr3, "movq %cr3, %rax"); >> DEF_NATIVE(pv_mmu_ops, write_cr3, "movq %rdi, %cr3"); >> @@ -50,7 +49,6 @@ unsigned native_patch(u8 type, u16 clobbers, void >*ibuf, >> PATCH_SITE(pv_irq_ops, save_fl); >> PATCH_SITE(pv_irq_ops, irq_enable); >> PATCH_SITE(pv_irq_ops, irq_disable); >> - PATCH_SITE(pv_cpu_ops, iret); >> PATCH_SITE(pv_cpu_ops, irq_enable_sysexit); >> PATCH_SITE(pv_cpu_ops, usergs_sysret32); >> PATCH_SITE(pv_cpu_ops, usergs_sysret64); -- Sent from my mobile phone. 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