[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Xen PV breakage after IRQ stack code refactoring
On 11/27/2017 12:34 AM, Juergen Gross wrote: > On 27/11/17 05:03, Andy Lutomirski wrote: >> On Sun, Nov 26, 2017 at 9:10 AM, Boris Ostrovsky >> <boris.ostrovsky@xxxxxxxxxx> wrote: >>> Andy, >>> >>> (Can't find the original patch in my mailbox) >>> >>> This hunk from 1d3e53e8624a ("x86/entry/64: Refactor IRQ stacks and make >>> them NMI-safe") >>> >>> >>> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S >>> index a9a8027..0d4483a 100644 >>> --- a/arch/x86/entry/entry_64.S >>> +++ b/arch/x86/entry/entry_64.S >>> @@ -447,6 +447,59 @@ ENTRY(irq_entries_start) >>> .endr >>> END(irq_entries_start) >>> >>> +.macro DEBUG_ENTRY_ASSERT_IRQS_OFF >>> +#ifdef CONFIG_DEBUG_ENTRY >>> + pushfq >>> + testl $X86_EFLAGS_IF, (%rsp) >>> + jz .Lokay_\@ >>> + ud2 >>> +.Lokay_\@: >>> + addq $8, %rsp >>> +#endif >>> +.endm >>> + >>> >>> makes Xen PV guests somewhat unhappy because IF flag will be set. >>> >>> I was hoping to use ALTERNATIVE instruction but when we hit this for the >>> first time we haven't rewritten instructions yet. Moving check_bugs() a bit >>> higher helps but because this is common code I don't know how well it will >>> work on other architectures (and, in fact, whether it is even safe on x86 in >>> general, although that can be verified). >>> >>> Another option is to also add a parameter to DEBUG_ENTRY_ASSERT_IRQS_OFF (or >>> to ENTER_IRQ_STACK) from xen_do_hypervisor_callback (which is where the >>> failure happens) but this looks pretty fragile in that it assumes that >>> xen_do_hypervisor_callback is the only place where we use this codepath >>> before alt instructions are set. >>> >>> Any other suggestions? >> Do we have a convenient asm way to access the save_fl pvop? > No, but adding it would be pretty straight forward. Its something like: > > #define SAVE_FLAGS(clobbers) \ > PARA_SITE(PARA_PATCH(pv_irq_ops, PV_IRQ_save_fl), clobbers, \ > PV_SAVE_REGS(clobbers | CLBR_CALLEE_SAVE); \ > call PARA_INDIRECT(pv_irq_ops+PV_IRQ_save_fl); \ > PV_RESTORE_REGS(clobbers | CLBR_CALLEE_SAVE);) > > similar to DISABLE_INTERRUPTS(), requiring just the definition of > PV_IRQ_save_fl in asm-offsets.c and the non-pvops definition of > SAVE_FLAGS() in irqflags.h. Hmm.. Indeed, I haven't thought of this for whatever reasons. I'll send the patch soon. Thanks. -boris _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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