Re: [PATCH v6 05/10] x86/tdx: Handle port I/O

[Kuppuswamy, Sathyanarayanan]

On 9/23/21 9:32 AM, Tom Lendacky wrote:
> On 9/22/21 5:52 PM, Kuppuswamy Sathyanarayanan wrote:
> > From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> >
> > TDX hypervisors cannot emulate instructions directly. This includes
> > port IO which is normally emulated in the hypervisor. All port IO
> > instructions inside TDX trigger the #VE exception in the guest and
> > would be normally emulated there.
> >
> > Also string I/O is not supported in TDX guest. So, unroll the string
> > I/O operation into a loop operating on one element at a time. This
> > method is similar to AMD SEV, so just extend the support for TDX guest
> > platform.
> >
> > Add a new confidential guest flag CC_ATTR_GUEST_UNROLL_STRING_IO to
> > add string unroll support in asm/io.h
> >
> > Co-developed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
> > Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> > Reviewed-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> > Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> > ---
> >
> > Changes since v5:
> >   * Changed prot_guest_has() to cc_platform_has().
> >
> > Changes since v4:
> >   * Changed order of variable declaration in tdx_handle_io().
> >   * Changed tdg_* prefix with tdx_*.
> >
> > Changes since v3:
> >   * Included PATTR_GUEST_UNROLL_STRING_IO protected guest flag
> >     addition change in this patch.
> >   * Rebased on top of Tom Lendacks protected guest change.
> >
> > Changes since v2:
> >   * None
> >
> > Changes since v1:
> >   * Fixed comments for tdg_handle_io().
> >   * Used _tdx_hypercall() instead of __tdx_hypercall() in tdg_handle_io().
> >
> >   arch/x86/include/asm/io.h   |  7 +++++--
> >   arch/x86/kernel/cpu/intel.c |  1 +
> >   arch/x86/kernel/tdx.c       | 35 +++++++++++++++++++++++++++++++++++
> >   include/linux/cc_platform.h | 11 +++++++++++
> >   4 files changed, 52 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
> > index fa6aa43e5dc3..67e0c4a0a0f4 100644
> > --- a/arch/x86/include/asm/io.h
> > +++ b/arch/x86/include/asm/io.h
> > @@ -40,6 +40,7 @@
> >   #include <linux/string.h>
> >   #include <linux/compiler.h>
> > +#include <linux/cc_platform.h>
> >   #include <asm/page.h>
> >   #include <asm/tdx.h>
> >   #include <asm/early_ioremap.h>
> > @@ -310,7 +311,8 @@ static inline unsigned type in##bwl##_p(int port)            \
> >                                       \
> >   static inline void outs##bwl(int port, const void *addr, unsigned long count) \
> >   {                                    \
> > -    if (sev_key_active()) {                        \ > +    if (sev_key_active() 
> > ||                        \
> > +        cc_platform_has(CC_ATTR_GUEST_UNROLL_STRING_IO)) {        \
>
> Would it make sense to make sev_key_active() and sev_enable_key generic and just re-use those 
> instead of adding CC_ATTR_GUEST_UNROLL_STRING_IO and having multiple conditions here?
>
> You can set the key in the TDX init routine just like SEV does.

Any reason for using sev_enable_key over CC attribute? IMO, CC attribute exist
to generalize the common feature code. My impression is SEV is specific to AMD
code.

> Thanks,
> Tom

--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer