[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v12 19/37] x86/fred: Update MSR_IA32_FRED_RSP0 during task switch
On November 13, 2023 4:37:42 AM EST, Borislav Petkov <bp@xxxxxxxxx> wrote: >On Mon, Oct 02, 2023 at 11:24:40PM -0700, Xin Li wrote: >> From: "H. Peter Anvin (Intel)" <hpa@xxxxxxxxx> >> >> 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. >> >> Signed-off-by: H. Peter Anvin (Intel) <hpa@xxxxxxxxx> >> Tested-by: Shan Kang <shan.kang@xxxxxxxxx> >> Signed-off-by: Xin Li <xin3.li@xxxxxxxxx> >> --- >> arch/x86/include/asm/switch_to.h | 8 ++++++-- >> 1 file changed, 6 insertions(+), 2 deletions(-) >> >> diff --git a/arch/x86/include/asm/switch_to.h >> b/arch/x86/include/asm/switch_to.h >> index f42dbf17f52b..c3bd0c0758c9 100644 >> --- a/arch/x86/include/asm/switch_to.h >> +++ b/arch/x86/include/asm/switch_to.h >> @@ -70,9 +70,13 @@ 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)) { >> + /* WRMSRNS is a baseline feature for FRED. */ >> + wrmsrns(MSR_IA32_FRED_RSP0, (unsigned >> long)task_stack_page(task) + THREAD_SIZE); > >If this non-serializing write happens now and, AFAICT, the CR3 write >during the task switch has already happened in switch_mm* earlier, what >is the serialization point that's going to make sure that write is >committed before the new task starts executing? > >Thx. > A resource cannot be consumed after the value has been written; this is the only necessary level of serialization, equivalent to, say, RAX. A serializing instruction stops the entire pipeline until everything has retired and any stores have become globally visible.
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