[Xen-devel] [patch 01/60] x86/entry/64/paravirt: Use paravirt-safe macro to access eflags

[Thomas Gleixner <tglx@xxxxxxxxxxxxx>]

From: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>

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@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: jgross@xxxxxxxx
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
Cc: luto@xxxxxxxxxx
Link: 
https://lkml.kernel.org/r/1512159805-6314-1-git-send-email-boris.ostrovsky@xxxxxxxxxx

---
V3:
* Use CLBR_RAX to preserve all registers except %rax


 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..18474bb 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_RAX)
+       testl $X86_EFLAGS_IF, %eax
        jz .Lokay_\@
        ud2
 .Lokay_\@:
-       addq $8, %rsp
+       popq %rax
 #endif
 .endm
 
diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/irqflags.h
index c8ef23f..89f0895 100644
--- a/arch/x86/include/asm/irqflags.h
+++ b/arch/x86/include/asm/irqflags.h
@@ -142,6 +142,9 @@ static inline notrace unsigned long 
arch_local_irq_save(void)
        swapgs;                                 \
        sysretl
 
+#ifdef CONFIG_DEBUG_ENTRY
+#define SAVE_FLAGS(x)          pushfq; popq %rax
+#endif
 #else
 #define INTERRUPT_RETURN               iret
 #define ENABLE_INTERRUPTS_SYSEXIT      sti; sysexit
diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 283efca..892df37 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -927,6 +927,15 @@ static inline notrace unsigned long 
arch_local_irq_save(void)
        PARA_SITE(PARA_PATCH(pv_cpu_ops, PV_CPU_usergs_sysret64),       \
                  CLBR_NONE,                                            \
                  jmp PARA_INDIRECT(pv_cpu_ops+PV_CPU_usergs_sysret64))
+
+#ifdef CONFIG_DEBUG_ENTRY
+#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);)
+#endif
+
 #endif /* CONFIG_X86_32 */
 
 #endif /* __ASSEMBLY__ */
diff --git a/arch/x86/kernel/asm-offsets_64.c b/arch/x86/kernel/asm-offsets_64.c
index 630212f..e3a5175 100644
--- a/arch/x86/kernel/asm-offsets_64.c
+++ b/arch/x86/kernel/asm-offsets_64.c
@@ -23,6 +23,9 @@ int main(void)
 #ifdef CONFIG_PARAVIRT
        OFFSET(PV_CPU_usergs_sysret64, pv_cpu_ops, usergs_sysret64);
        OFFSET(PV_CPU_swapgs, pv_cpu_ops, swapgs);
+#ifdef CONFIG_DEBUG_ENTRY
+       OFFSET(PV_IRQ_save_fl, pv_irq_ops, save_fl);
+#endif
        BLANK();
 #endif
 
-- 
1.7.1





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