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

[Tom Lendacky]

On 9/23/21 12:24 PM, Kuppuswamy, Sathyanarayanan wrote:
> 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.

When the SEV series was initially submitted, it originally did an 
sev_active() check. For various reasons a static key and the 
sev_key_active() call was requested.

My suggestion was to change the name to something that doesn't have 
SEV/sev in it that can be used by both SEV and TDX. The sev_enable_key can 
be moved to a common file (maybe cc_platform.c) and renamed. Then 
arch/x86/include/asm/io.h can change the #ifdef from 
CONFIG_AMD_MEM_ENCRYPT to CONFIG_ARCH_HAS_CC_PLATFORM.

Not sure if anyone else feels the same, though, so just my suggestion.

Thanks,
Tom

> > Thanks,
> > Tom