Messages in this thread | | | Date | Mon, 20 Mar 2023 17:52:33 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v5 23/34] x86/fred: update MSR_IA32_FRED_RSP0 during task switch |
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On Mon, Mar 06, 2023 at 06:39:35PM -0800, Xin Li wrote: > From: "H. Peter Anvin (Intel)" <hpa@zytor.com> > > MSR_IA32_FRED_RSP0 is used during ring 3 event delivery, and needs to > be updated to point to the top of next task stack during task switch. > > Update MSR_IA32_FRED_RSP0 with WRMSR instruction for now, and will use > WRMSRNS/WRMSRLIST for performance once it gets upstreamed. > > Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com> > Tested-by: Shan Kang <shan.kang@intel.com> > Signed-off-by: Xin Li <xin3.li@intel.com> > --- > arch/x86/include/asm/switch_to.h | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/include/asm/switch_to.h b/arch/x86/include/asm/switch_to.h > index 5c91305d09d2..00fd85abc1d2 100644 > --- a/arch/x86/include/asm/switch_to.h > +++ b/arch/x86/include/asm/switch_to.h > @@ -68,9 +68,16 @@ static inline void update_task_stack(struct task_struct *task) > #ifdef CONFIG_X86_32 > this_cpu_write(cpu_tss_rw.x86_tss.sp1, task->thread.sp0); > #else > - /* Xen PV enters the kernel on the thread stack. */ > - if (cpu_feature_enabled(X86_FEATURE_XENPV)) > + if (cpu_feature_enabled(X86_FEATURE_FRED)) { > + /* > + * Will use WRMSRNS/WRMSRLIST for performance once it's upstreamed. > + */ > + wrmsrl(MSR_IA32_FRED_RSP0, > + task_top_of_stack(task) + TOP_OF_KERNEL_STACK_PADDING); > + } else if (cpu_feature_enabled(X86_FEATURE_XENPV)) {
Whee, so hardware will really only ever look at this when RSP0? I don't need to worry about exceptions during context switch?
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