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Message-ID: <fb622b26-acb0-3203-51fe-62bfa1b5cc5b@oracle.com> Date: Fri, 1 Dec 2017 11:57:21 -0500 From: Boris Ostrovsky <boris.ostrovsky@...cle.com> To: Andy Lutomirski <luto@...nel.org> Cc: "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>, Juergen Gross <jgross@...e.com> Subject: Re: [PATCH v2] x86/entry/64/paravirt: Use paravirt-safe macro to access eflags On 12/01/2017 11:22 AM, Andy Lutomirski wrote: > On Tue, Nov 28, 2017 at 7:28 AM, Boris Ostrovsky > <boris.ostrovsky@...cle.com> wrote: >> Commit 1d3e53e8624a ("x86/entry/64: Refactor IRQ stacks and make >> them NMI-safe") added DEBUG_ENTRY_ASSERT_IRQS_OFF macro that acceses >> eflags using 'pushfq' instruction when testing for IF bit. On PV Xen >> guests looking at IF flag directly will always see it set, resulting >> in 'ud2'. >> >> Introduce SAVE_FLAGS() macro that will use appropriate save_fl pv op >> when running paravirt. >> >> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com> >> --- >> V2: >> * Preserve %rax in DEBUG_ENTRY_ASSERT_IRQS_OFF >> * Return (pop) %rax in SAVE_FLAGS for !CONFIG_PARAVIRT (irqflags.h) >> >> arch/x86/entry/entry_64.S | 7 ++++--- >> arch/x86/include/asm/irqflags.h | 3 +++ >> arch/x86/include/asm/paravirt.h | 9 +++++++++ >> arch/x86/kernel/asm-offsets_64.c | 3 +++ >> 4 files changed, 19 insertions(+), 3 deletions(-) >> >> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S >> index f81d50d..c208dc1 100644 >> --- a/arch/x86/entry/entry_64.S >> +++ b/arch/x86/entry/entry_64.S >> @@ -466,12 +466,13 @@ END(irq_entries_start) >> >> .macro DEBUG_ENTRY_ASSERT_IRQS_OFF >> #ifdef CONFIG_DEBUG_ENTRY >> - pushfq >> - testl $X86_EFLAGS_IF, (%rsp) >> + pushq %rax >> + SAVE_FLAGS(CLBR_ANY) >> + testl $X86_EFLAGS_IF, %eax > Confused. You're both using CLBR_ANY and RAX. Did you perhaps mean CLBR_NONE? CLBR_NONE will restore all registers, won't it? So it should be CLBR_RAX, should it? Otherwise we'll lose return value. -boris > >> jz .Lokay_\@ >> ud2 >> .Lokay_\@: >> - addq $8, %rsp >> + popq %rax >> #endif >> .endm >> >>
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