Re: [Xen-devel] [PATCH] x86/HVM: adjust hvm_interrupt_blocked()

["Roger Pau Monné" <roger.pau@citrix.com>]

On Thu, Aug 31, 2023 at 12:42:58PM +0200, Roger Pau Monné wrote:
> On Fri, Oct 12, 2018 at 09:58:46AM -0600, Jan Beulich wrote:
> > First of all, hvm_intsrc_mce was not considered here at all, yet nothing
> > blocks #MC (other than an already in-progress #MC, but dealing with this
> > is not the purpose of this patch).
> > 
> > Additionally STI-shadow only blocks maskable interrupts, but not NMI.
> 
> I've found the Table 25-3 on Intel SDM vol3 quite helpful:
> 
> "Execution of STI with RFLAGS.IF = 0 blocks maskable interrupts on the
> instruction boundary following its execution.1 Setting this bit
> indicates that this blocking is in effect."
> 
> And:
> 
> "Execution of a MOV to SS or a POP to SS blocks or suppresses certain
> debug exceptions as well as interrupts (maskable and nonmaskable) on
> the instruction boundary following its execution."
> 
> Might be worth adding to the commit message IMO.

So I've found a further footnote that contains:

"Nonmaskable interrupts and system-management interrupts may also be
inhibited on the instruction boundary following such an execution of
STI."

So we want to take the more restrictive implementation of STI-shadow,
and block #NMI there also.

Thanks, Roger.