From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: [Patch 1/3 v2] x86/irq: local_irq_restore() should not blindly popf Date: Mon, 21 Oct 2013 19:30:14 +0100 Message-ID: <526572B6.3030803@citrix.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Keir Fraser Cc: Jan Beulich , Xen-devel List-Id: xen-devel@lists.xenproject.org On 21/10/13 19:18, Keir Fraser wrote: > On 21/10/2013 17:33, "Andrew Cooper" wrote: > >> local_irq_restore() should only be concerned with possibly changing the >> interrupt flag. A blind popf could corrupt other system flags. >> >> While playing in this area, fixup an opencoded use of X86_EFLAGS_IF. >> >> Signed-off-by: Andrew Cooper >> CC: Keir Fraser >> CC: Jan Beulich >> >> --- >> >> This is rather more RFC. It boots and runs VMs, so I am fairly sure it is >> functionally correct, but I cant help feeling there might be a neater way to >> do the inline assembly. Suggestions welcome. >> --- >> xen/include/asm-x86/system.h | 11 ++++++++--- >> 1 file changed, 8 insertions(+), 3 deletions(-) >> >> diff --git a/xen/include/asm-x86/system.h b/xen/include/asm-x86/system.h >> index 6ab7d56..ff52671 100644 >> --- a/xen/include/asm-x86/system.h >> +++ b/xen/include/asm-x86/system.h >> @@ -3,6 +3,7 @@ >> >> #include >> #include >> +#include >> >> #define read_segment_register(name) \ >> ({ u16 __sel; \ >> @@ -159,15 +160,19 @@ static always_inline unsigned long __cmpxchg( >> #define local_irq_restore(x) \ >> ({ \ >> BUILD_BUG_ON(sizeof(x) != sizeof(long)); \ >> - asm volatile ( "push" __OS " %0 ; popf" __OS \ >> - : : "g" (x) : "memory", "cc" ); \ >> + asm volatile ( \ >> + "pushf" __OS "\n\t" \ >> + "and" __OS " %0, (%%" __OP "sp)\n\t" \ >> + "orw %1, (%%" __OP "sp)\n\t" \ >> + "popf" __OS "\n\t" : : "g" ( ~X86_EFLAGS_IF ), \ > Would this be better as a constant constraint ("i")? I was wondering what the best practice for this would be. In most cases, I would imagine that an immediate would be used. However, as this is a define and therefore forcibly inlined everywhere it is used, it is just possible that the compiler could find a ~X86_EFLAGS_IF already in context, and optimise down to an "and r64,r/m64". ~Andrew > >> + "g" ( x & X86_EFLAGS_IF ) ); \ >> }) >> >> static inline int local_irq_is_enabled(void) >> { >> unsigned long flags; >> local_save_flags(flags); >> - return !!(flags & (1<<9)); /* EFLAGS_IF */ >> + return !!(flags & X86_EFLAGS_IF); >> } >> >> #define BROKEN_ACPI_Sx 0x0001 >