On 04/06/18 14:59, Andrew Cooper wrote:
> See the code comment for the details.
>
> Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com>
> ---
> CC: Jan Beulich <jbeul...@suse.com>
> CC: Jun Nakajima <jun.nakaj...@intel.com>
> CC: Kevin Tian <kevin.t...@intel.com>
>
> Jun/Kevin: This workaround is as suggested by Gil, and there is expected to be
> an SDM update discussing the corner case.
>
> Note that, like elsewhere dealing with eflags.tf, this is probably buggy in
> combination with MSR_DEBUGCTL.BTF. I'll untangle the BTF swamp at some later
> point.
> ---
> xen/arch/x86/hvm/vmx/vmx.c | 30 ++++++++++++++++++++++++++++++
> 1 file changed, 30 insertions(+)
>
> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
> index 82ef3aa..58ff8c7 100644
> --- a/xen/arch/x86/hvm/vmx/vmx.c
> +++ b/xen/arch/x86/hvm/vmx/vmx.c
> @@ -1794,6 +1794,36 @@ static void vmx_inject_event(const struct x86_event
> *event)
> write_debugreg(6, merge_dr6(read_debugreg(6), event->pending_dbg,
> curr->domain->arch.cpuid->feat.rtm));
>
> + /*
> + * Work around SS/STI vmentry bug.
> + *
> + * If kernel code is single stepping itself and executes an STI
> + * instruction resulting in an STI shadow, a vmexit occurs due to #DB
> + * interception, but the vmentry fails due to a failed consistency
> + * check. (Hardware comes to the conclusion that there should be a
> + * pending debug exception, but doesn't account for the pending #DB
> in
> + * VMENTRY_INTR_INFO.)
> + *
> + * Manually adjust the pending debug exception field to mark BS as
> + * pending, which satisfies the consistency check and allows the
> + * vmentry to succeed.
> + */
> + if ( unlikely(regs->eflags & X86_EFLAGS_TF) )
> + {
> + unsigned long int_info;
> +
> + __vmread(GUEST_INTERRUPTIBILITY_INFO, &int_info);
> +
> + if ( int_info & VMX_INTR_SHADOW_STI )
> + {
> + unsigned long pending_dbg;
> +
> + __vmread(GUEST_PENDING_DBG_EXCEPTIONS, &pending_dbg);
> + __vmwrite(GUEST_PENDING_DBG_EXCEPTIONS,
> + pending_dbg | X86_DR6_BS);
> + }
> + }
> +
> if ( !nestedhvm_vcpu_in_guestmode(curr) ||
> !nvmx_intercepts_exception(curr, TRAP_debug, _event.error_code)
> )
> {
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