Messages in this thread | | | From | Jue Wang <> | Date | Fri, 18 Feb 2022 08:03:24 -0800 | Subject | Re: [PATCH v2] x86/mce: work around an erratum on fast string copy instructions. |
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On Fri, Feb 18, 2022 at 7:07 AM Borislav Petkov <bp@alien8.de> wrote: > > On Thu, Feb 17, 2022 at 05:32:09PM -0800, Jue Wang wrote: > > +static noinstr bool quirk_skylake_repmov(void) > > +{ > > + u64 mcgstatus = mce_rdmsrl(MSR_IA32_MCG_STATUS); > > + u64 misc_enable = __rdmsr(MSR_IA32_MISC_ENABLE); > > + > > + /* > > + * Apply the quirk only to local machine checks, i.e., no broadcast > > + * sync is needed. > > + */ > > + if ((mcgstatus & MCG_STATUS_LMCES) && > > + unlikely(misc_enable & MSR_IA32_MISC_ENABLE_FAST_STRING)) { > > + u64 mc1_status = mce_rdmsrl(MSR_IA32_MCx_STATUS(1)); > > + > > + /* Check for a software-recoverable data fetch error. */ > > + if ((mc1_status & > > + (MCI_STATUS_VAL | MCI_STATUS_OVER | MCI_STATUS_UC | MCI_STATUS_EN | > > + MCI_STATUS_ADDRV | MCI_STATUS_MISCV | MCI_STATUS_PCC | > > + MCI_STATUS_AR | MCI_STATUS_S)) == > > + (MCI_STATUS_VAL | MCI_STATUS_UC | MCI_STATUS_EN | > > + MCI_STATUS_ADDRV | MCI_STATUS_MISCV | > > + MCI_STATUS_AR | MCI_STATUS_S)) { > > + misc_enable &= ~MSR_IA32_MISC_ENABLE_FAST_STRING; > > + __wrmsr(MSR_IA32_MISC_ENABLE, > > + (u32)misc_enable, (u32)(misc_enable >> 32)); > > "You're going to have to use the mce_{rd,wr}msrl() routines." > > I actually really meant that. Thanks.
Since MSR_IA32_MISC_ENABLE is not a MCA register, I wonder if we want to mix its read/write with the injected MCE code. I was a bit concerned about potential race with mce-inject and the read/write to MSR_IA32_MISC_ENABLE.
> > And I went and simplified this a bit more so that it is more readable, > diff ontop. > > Also, Tony, I think the clearing of MCG_STATUS should happen last. > > --- > diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c > index c1a41da99975..1741be9b9464 100644 > --- a/arch/x86/kernel/cpu/mce/core.c > +++ b/arch/x86/kernel/cpu/mce/core.c > @@ -831,34 +831,35 @@ quirk_sandybridge_ifu(int bank, struct mce *m, struct pt_regs *regs) > */ > static noinstr bool quirk_skylake_repmov(void) > { > - u64 mcgstatus = mce_rdmsrl(MSR_IA32_MCG_STATUS); > - u64 misc_enable = __rdmsr(MSR_IA32_MISC_ENABLE); > + u64 mcgstatus = mce_rdmsrl(MSR_IA32_MCG_STATUS); > + u64 misc_enable = mce_rdmsrl(MSR_IA32_MISC_ENABLE); > + u64 mc1_status; > > /* > * Apply the quirk only to local machine checks, i.e., no broadcast > * sync is needed. > */ > - if ((mcgstatus & MCG_STATUS_LMCES) && > - (misc_enable & MSR_IA32_MISC_ENABLE_FAST_STRING)) { > - u64 mc1_status = mce_rdmsrl(MSR_IA32_MCx_STATUS(1)); > - > - /* Check for a software-recoverable data fetch error. */ > - if ((mc1_status & > - (MCI_STATUS_VAL | MCI_STATUS_OVER | MCI_STATUS_UC | MCI_STATUS_EN | > - MCI_STATUS_ADDRV | MCI_STATUS_MISCV | MCI_STATUS_PCC | > - MCI_STATUS_AR | MCI_STATUS_S)) == > - (MCI_STATUS_VAL | MCI_STATUS_UC | MCI_STATUS_EN | > - MCI_STATUS_ADDRV | MCI_STATUS_MISCV | > - MCI_STATUS_AR | MCI_STATUS_S)) { > - misc_enable &= ~MSR_IA32_MISC_ENABLE_FAST_STRING; > - __wrmsr(MSR_IA32_MISC_ENABLE, > - (u32)misc_enable, (u32)(misc_enable >> 32)); > - mce_wrmsrl(MSR_IA32_MCG_STATUS, 0); > - mce_wrmsrl(MSR_IA32_MCx_STATUS(1), 0); > - pr_err_once("Errata detected, disable fast string copy instructions.\n"); > - return true; > - } > + if (!(mcgstatus & MCG_STATUS_LMCES) || > + !(misc_enable & MSR_IA32_MISC_ENABLE_FAST_STRING)) > + return false; > + > + mc1_status = mce_rdmsrl(MSR_IA32_MCx_STATUS(1)); > + > + /* Check for a software-recoverable data fetch error. */ > + if ((mc1_status & > + (MCI_STATUS_VAL | MCI_STATUS_OVER | MCI_STATUS_UC | MCI_STATUS_EN | > + MCI_STATUS_ADDRV | MCI_STATUS_MISCV | MCI_STATUS_PCC | > + MCI_STATUS_AR | MCI_STATUS_S)) == > + (MCI_STATUS_VAL | MCI_STATUS_UC | MCI_STATUS_EN | > + MCI_STATUS_ADDRV | MCI_STATUS_MISCV | > + MCI_STATUS_AR | MCI_STATUS_S)) { > + misc_enable &= ~MSR_IA32_MISC_ENABLE_FAST_STRING; > + mce_wrmsrl(MSR_IA32_MISC_ENABLE, misc_enable); > + mce_wrmsrl(MSR_IA32_MCx_STATUS(1), 0); > + pr_err_once("Erratum detected, disable fast string copy instructions.\n"); > + return true; > } > + > return false; > } > > @@ -1432,7 +1433,7 @@ noinstr void do_machine_check(struct pt_regs *regs) > return unexpected_machine_check(regs); > > if (mce_flags.skx_repmov_quirk && quirk_skylake_repmov()) > - return; > + goto clear; > > /* > * Establish sequential order between the CPUs entering the machine > @@ -1576,6 +1577,7 @@ noinstr void do_machine_check(struct pt_regs *regs) > out: > instrumentation_end(); > > +clear: > mce_wrmsrl(MSR_IA32_MCG_STATUS, 0); > } > EXPORT_SYMBOL_GPL(do_machine_check); > > -- > Regards/Gruss, > Boris. > > https://people.kernel.org/tglx/notes-about-netiquette
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