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SubjectRe: [PATCH v6 05/10] x86/tdx: Handle port I/O
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On 9/22/21 5:52 PM, Kuppuswamy Sathyanarayanan wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
>
> 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@linux.intel.com>
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Reviewed-by: Andi Kleen <ak@linux.intel.com>
> Reviewed-by: Dan Williams <dan.j.williams@intel.com>
> ---
>
> 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.

Thanks,
Tom

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