[Xen-devel] Re: [PATCH 2/6] MCE: Not GP fault when guest write non 0s or 1s to MCA CTL MSRs.

[Christoph Egger <Christoph.Egger@xxxxxxx>]

On Thursday 28 January 2010 10:48:40 Jiang, Yunhong wrote:
> >-----Original Message-----
> >From: Christoph Egger [mailto:Christoph.Egger@xxxxxxx]
> >Sent: Thursday, January 28, 2010 4:12 PM
> >To: Jiang, Yunhong
> >Cc: Keir Fraser; Frank.Vanderlinden@xxxxxxx; Jan Beulich;
> >xen-devel@xxxxxxxxxxxxxxxxxxx
> >Subject: Re: [PATCH 2/6] MCE: Not GP fault when guest write non 0s or 1s
> > to MCA CTL MSRs.
> >
> >On Thursday 28 January 2010 06:55:53 Jiang, Yunhong wrote:
> >> Not GP fault when guest write non 0s or 1s to MCA CTL MSRs.
> >>
> >> a) For Mci_CTL MSR, Guest can write any value to it. When read back, it
> >> will be ANDed with the physical value. Some bit in physical value can be
> >> 0, either because read-only in hardware (like masked by AMD's
> >> Mci_CTL_MASK), or because Xen didn't enable it. If guest write some bit
> >> as 0, while that bit is 1 in host, we will not inject MCE corresponding
> >> that bank to guest, as we can't distinguish if the MCE is caused by the
> >> guest-cleared bit.
> >>
> >> b) For MCG_CTL MSR, guest can write any value to it. When read back, it
> >> will be ANDed with the physical value. If guest does not write all 1s.
> >> In mca_ctl_conflict(), we simply not inject any vMCE to guest if some
> >> bit is set in physical MSR while is cleared in guest 's vMCG_CTL MSR.
> >>
> >> Signed-off-by: Jiang, Yunhong <yunhong.jiang@xxxxxxxxx>
> >>
> >>
> >> diff -r b2a7600b71cc xen/arch/x86/cpu/mcheck/mce.c
> >> --- a/xen/arch/x86/cpu/mcheck/mce.c        Tue Jan 26 00:52:19 2010 +0800
> >> +++ b/xen/arch/x86/cpu/mcheck/mce.c        Tue Jan 26 00:57:19 2010 +0800
> >> @@ -30,6 +30,11 @@ unsigned int nr_mce_banks;
> >>  unsigned int nr_mce_banks;
> >>
> >>  static uint64_t g_mcg_cap;
> >> +
> >> +/* Real value in physical CTL MSR */
> >> +static uint64_t h_mcg_ctl = 0UL;
> >> +static uint64_t *h_mci_ctrl;
> >> +int firstbank;
> >
> >The physical MSRs are per physical cpu-core on AMD CPUs.
> >The data structure does not reflect this.
> >
> >Other than that this patch is fine with me.
>
> Christoph, thanks for your review very much.
>
> Yes, the MSRs are mostly per cpu-core in Intel side also, although some
> sharing may happen. On AMD platform, will different CPU has different ctrl
> value?

This is possible. If this actually happens or not depends on what Xen is 
doing.

Christoph

> Or will Xen setup different value to different CPU? I assume they 
> should be same, am I right?
>
> Thanks
> --jyh
>
> >Christoph
> >
> >>  static void intpose_init(void);
> >>  static void mcinfo_clear(struct mc_info *);
> >> @@ -642,6 +647,21 @@ void mcheck_init(struct cpuinfo_x86 *c)
> >>            break;
> >>    }
> >>
> >> +    if ( !h_mci_ctrl )
> >> +    {
> >> +        h_mci_ctrl = xmalloc_array(uint64_t, nr_mce_banks);
> >> +        if (!h_mci_ctrl)
> >> +        {
> >> +            dprintk(XENLOG_INFO, "Failed to alloc h_mci_ctrl\n");
> >> +            return;
> >> +        }
> >> +        /* Don't care banks before firstbank */
> >> +        memset(h_mci_ctrl, 0xff, sizeof(h_mci_ctrl));
> >> +        for (i = firstbank; i < nr_mce_banks; i++)
> >> +            rdmsrl(MSR_IA32_MC0_CTL + 4*i, h_mci_ctrl[i]);
> >> +    }
> >> +    if (g_mcg_cap & MCG_CTL_P)
> >> +        rdmsrl(MSR_IA32_MCG_CTL, h_mcg_ctl);
> >>      set_poll_bankmask(c);
> >>    if (!inited)
> >>            printk(XENLOG_INFO "CPU%i: No machine check initialization\n",
> >> @@ -708,7 +728,8 @@ int mce_rdmsr(uint32_t msr, uint64_t *va
> >>              *val);
> >>          break;
> >>      case MSR_IA32_MCG_CTL:
> >> -        *val = d->arch.vmca_msrs.mcg_ctl;
> >> +        /* Always 0 if no CTL support */
> >> +        *val = d->arch.vmca_msrs.mcg_ctl & h_mcg_ctl;
> >>          mce_printk(MCE_VERBOSE, "MCE: rdmsr MCG_CTL 0x%"PRIx64"\n",
> >>              *val);
> >>          break;
> >> @@ -723,7 +744,8 @@ int mce_rdmsr(uint32_t msr, uint64_t *va
> >>          switch (msr & (MSR_IA32_MC0_CTL | 3))
> >>          {
> >>          case MSR_IA32_MC0_CTL:
> >> -            *val = d->arch.vmca_msrs.mci_ctl[bank];
> >> +            *val = d->arch.vmca_msrs.mci_ctl[bank] &
> >> +                    (h_mci_ctrl ? h_mci_ctrl[bank] : ~0UL);
> >>              mce_printk(MCE_VERBOSE, "MCE: rdmsr MC%u_CTL
> >
> >0x%"PRIx64"\n",
> >
> >>                       bank, *val);
> >>              break;
> >> @@ -805,13 +827,6 @@ int mce_wrmsr(u32 msr, u64 val)
> >>      switch ( msr )
> >>      {
> >>      case MSR_IA32_MCG_CTL:
> >> -        if ( val && (val + 1) )
> >> -        {
> >> -            mce_printk(MCE_QUIET, "MCE: val \"%"PRIx64"\" written "
> >> -                     "to MCG_CTL should be all 0s or 1s\n", val);
> >> -            ret = -1;
> >> -            break;
> >> -        }
> >>          d->arch.vmca_msrs.mcg_ctl = val;
> >>          break;
> >>      case MSR_IA32_MCG_STATUS:
> >> @@ -855,14 +870,6 @@ int mce_wrmsr(u32 msr, u64 val)
> >>          switch ( msr & (MSR_IA32_MC0_CTL | 3) )
> >>          {
> >>          case MSR_IA32_MC0_CTL:
> >> -            if ( val && (val + 1) )
> >> -            {
> >> -                mce_printk(MCE_QUIET, "MCE: val written to MC%u_CTL "
> >> -                         "should be all 0s or 1s (is %"PRIx64")\n",
> >> -                         bank, val);
> >> -                ret = -1;
> >> -                break;
> >> -            }
> >>              d->arch.vmca_msrs.mci_ctl[bank] = val;
> >>              break;
> >>          case MSR_IA32_MC0_STATUS:
> >> @@ -1162,6 +1169,23 @@ void intpose_inval(unsigned int cpu_nr,
> >>      (r) <= MSR_IA32_MC0_MISC + (nr_mce_banks - 1) * 4 && \
> >>      ((r) - MSR_IA32_MC0_CTL) % 4 != 0)    /* excludes MCi_CTL */
> >>
> >> +int mca_ctl_conflict(struct mcinfo_bank *bank, struct domain *d)
> >> +{
> >> +    int bank_nr;
> >> +
> >> +    if ( !bank || !d || !h_mci_ctrl )
> >> +        return 1;
> >> +
> >> +    /* Will MCE happen in host if If host mcg_ctl is 0? */
> >> +    if ( ~d->arch.vmca_msrs.mcg_ctl & h_mcg_ctl )
> >> +        return 1;
> >> +
> >> +    bank_nr = bank->mc_bank;
> >> +    if (~d->arch.vmca_msrs.mci_ctl[bank_nr] & h_mci_ctrl[bank_nr] )
> >> +        return 1;
> >> +    return 0;
> >> +}
> >> +
> >>  static int x86_mc_msrinject_verify(struct xen_mc_msrinject *mci)
> >>  {
> >>    struct cpuinfo_x86 *c;
> >> diff -r b2a7600b71cc xen/arch/x86/cpu/mcheck/mce.h
> >> --- a/xen/arch/x86/cpu/mcheck/mce.h        Tue Jan 26 00:52:19 2010 +0800
> >> +++ b/xen/arch/x86/cpu/mcheck/mce.h        Tue Jan 26 00:52:20 2010 +0800
> >> @@ -39,6 +39,8 @@ void amd_nonfatal_mcheck_init(struct cpu
> >>  void amd_nonfatal_mcheck_init(struct cpuinfo_x86 *c);
> >>
> >>  u64 mce_cap_init(void);
> >> +extern int firstbank;
> >> +int mca_ctl_conflict(struct mcinfo_bank *bank, struct domain *d);
> >>
> >>  int intel_mce_rdmsr(uint32_t msr, uint64_t *val);
> >>  int intel_mce_wrmsr(uint32_t msr, uint64_t val);
> >> diff -r b2a7600b71cc xen/arch/x86/cpu/mcheck/mce_intel.c
> >> --- a/xen/arch/x86/cpu/mcheck/mce_intel.c  Tue Jan 26 00:52:19 2010 +0800
> >> +++ b/xen/arch/x86/cpu/mcheck/mce_intel.c  Tue Jan 26 00:52:20 2010 +0800
> >> @@ -20,7 +20,6 @@ int ser_support = 0;
> >>  int ser_support = 0;
> >>
> >>  static int nr_intel_ext_msrs = 0;
> >> -static int firstbank;
> >>
> >>  /* Below are for MCE handling */
> >>  struct mce_softirq_barrier {
> >> @@ -361,7 +360,15 @@ static void intel_UCR_handler(struct mci
> >>                         *  the mfn in question) */
> >>                        BUG_ON( result->owner == DOMID_COW );
> >>                        if ( result->owner != DOMID_XEN ) {
> >> +
> >>                            d = get_domain_by_id(result->owner);
> >> +                          if ( mca_ctl_conflict(bank, d) )
> >> +                          {
> >> +                              /* Guest has different MCE ctl with
> >> hypervisor */ +                              put_domain(d);
> >> +                              return;
> >> +                          }
> >> +
> >>                            gfn =
> >>                                mfn_to_gmfn(d, ((bank->mc_addr) >>
> >> PAGE_SHIFT)); bank->mc_addr =




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