Given that we don't properly virtualise/emulate machine check (we only set
the feature bit because some versions of Windows demand it) can we get away
with returning zero for reads of MCG_CAP?
-- Keir
On 27/8/07 20:11, "Ben Guthro" <bguthro@xxxxxxxxxxxxxxx> wrote:
> Intercept guest reads of MSR_IA32_MCG_CAP and limit the number of memory banks
> reported to one.
> This prevents us from trying to read status of non-existent banks when
> migrated to a machine
> with fewer banks.
>
> Signed-off-by: Ben Guthro
> Signed-off-by: David Lively <dlively@xxxxxxxxxxxxxxx>
>
> diff -r 4eea7c9b3bf2 xen/arch/x86/hvm/svm/svm.c
> --- a/xen/arch/x86/hvm/svm/svm.c Thu Aug 02 08:59:43 2007 -0400
> +++ b/xen/arch/x86/hvm/svm/svm.c Thu Aug 02 08:59:43 2007 -0400
> @@ -2162,7 +2162,19 @@ static void svm_do_msr_access(
> /* No point in letting the guest see real MCEs */
> msr_content = 0;
> break;
> -
> + case MSR_IA32_MCG_CAP:
> + if ( rdmsr_safe(ecx, regs->eax, regs->edx) == 0 ) {
> + /*
> + * Report at most one memory bank so migration to a machine
> with
> + * fewer banks doesn't cause guest GPFs when the guest tries
> to read the
> + * (now, after migration) non-existent banks' MSRs.
> + */
> + regs->eax = (regs->eax & ~0xFF) | !!(regs->eax & 0xFF);
> + goto done;
> + }
> + gdprintk(XENLOG_ERR, "%s: rdmsr_safe(MCG_CAP) failed!\n",
> __FUNCTION__);
> + svm_inject_exception(v, TRAP_gp_fault, 1, 0);
> + return;
> default:
> if ( rdmsr_hypervisor_regs(ecx, &eax, &edx) ||
> rdmsr_safe(ecx, eax, edx) == 0 )
> diff -r 4eea7c9b3bf2 xen/arch/x86/hvm/vmx/vmx.c
> --- a/xen/arch/x86/hvm/vmx/vmx.c Thu Aug 02 08:59:43 2007 -0400
> +++ b/xen/arch/x86/hvm/vmx/vmx.c Thu Aug 02 09:14:06 2007 -0400
> @@ -2754,6 +2754,19 @@ static int vmx_do_msr_read(struct cpu_us
> /* No point in letting the guest see real MCEs */
> msr_content = 0;
> break;
> + case MSR_IA32_MCG_CAP:
> + if ( rdmsr_safe(ecx, regs->eax, regs->edx) == 0 ) {
> + /*
> + * Report only a single memory bank so migration to a machine
> with
> + * fewer banks doesn't cause guest GPFs when the guest tries to
> read the
> + * (now, after migration) non-existent banks' MSRs.
> + */
> + regs->eax = (regs->eax & ~0xFF) | !!(regs->eax & 0xFF);
> + goto done;
> + }
> + gdprintk(XENLOG_ERR, "%s: rdmsr_safe(MCG_CAP) failed!\n",
> __FUNCTION__);
> + vmx_inject_hw_exception(v, TRAP_gp_fault, 0);
> + return 0;
> default:
> switch ( long_mode_do_msr_read(regs) )
> {
> _______________________________________________
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> Xen-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-devel
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