Re: [PATCH v4 0/2] x86/tdx: Use TDVMCALLs directly for earlyprintk

[Nikolay Borisov <nik.borisov@suse.com>]

On 6.10.26 г. 1:50 ч., Vishal Verma wrote:
> Background
> ==========
> 
> TDX guests have early_printk support, but it is through a roundabout way
> using a #VE exception as a functional mechanism. The exception handler
> has to use TDG.VP.VEINFO.GET to find out what faulted, and then issue
> the TDVMCALL. Simplify this by using a TDVMCALL from the guest which can
> directly perform the port I/O.
> 
> Patch details
> =============
> 
> Patch 1 is a cleanup that moves the port I/O direction constants to
> arch/x86/include/asm/shared/tdx.h.
> 
> Patch 2: Add a new earlyprintk=tdx option, which calls the new
> tdx_serial_in() / tdx_serial_out() helpers to perform the port I/O
> directly using TDVMCALLs.
> 
> The serial earlyprintk path is left as is - TD guests using this will
> still take a #VE exception, and the exception handler will perform the
> I/O.
> 
> Testing
> =======
> 
> Added a counter for the number of COM1 port I/O #VEs handled:
> 
>    no earlyprintk     -  ~63000
>    earlyprintk=ttyS0  -  ~61000
>    earlyprintk=tdx    -  ~35000
> 
> The new tdx option nearly halves the number of #VEs handled.
> 
> Additionally, ran the usual suite of CI testing, which covers KVM self
> tests, KVM unit tests, and Avocado KVM tests without any regressions.
> 
> Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
> ---
> Changes in v4:
> - Rename the tdx_inb()/tdx_outb() helpers directly to the serial
>    accessors with __noendbr annotations, and remove the config ifdefs
>    from early_printk.c. (Kiryl)
> - Rebase to v7.3-rc6
> - Link to v3: https://patch.msgid.link/20260922-b4-tdx_earlyprintk_tdcalls-v3-0-6ebaa599df10@intel.com
> 
> Changes in v3:
> - Drop the ttySN and baudrate option parsing for earlyprintk=tdx (Dave Hansen)
> - Link to v2: https://patch.msgid.link/20260921-b4-tdx_earlyprintk_tdcalls-v2-0-ad1fde3f25fd@intel.com
> 
> Changes in v2:
> - Rebase to v7.3-rc4
> - Move the TDX hypercall helpers into coco/tdx/tdx.c (Kiryl)
> - Add a new earlyprintk=tdx option that implements the direct TDVMCALL
>    path (Dave Hansen)
> - Link to v1: https://patch.msgid.link/20260910-b4-tdx_earlyprintk_tdcalls-v1-0-4b2b1bf9001b@intel.com
> 
> ---
> Vishal Verma (2):
>        x86/tdx: Move port I/O definitions to a shared header
>        x86/early_printk: Add earlyprintk=tdx to drive the UART with TDVMCALLs
> 
>   Documentation/admin-guide/kernel-parameters.txt |  8 ++++++
>   arch/x86/include/asm/shared/tdx.h               |  6 ++++
>   arch/x86/include/asm/tdx.h                      |  4 +++
>   arch/x86/boot/compressed/tdx.c                  |  4 +--
>   arch/x86/coco/tdx/tdx.c                         | 37 +++++++++++++++++++++----
>   arch/x86/kernel/early_printk.c                  | 20 +++++++++++++
>   6 files changed, 71 insertions(+), 8 deletions(-)
> ---
> base-commit: a90ee4305c4a5df72c11b31dacfdc76e00fcf78a
> change-id: 20260903-b4-tdx_earlyprintk_tdcalls-40d1b21a8ba2
> 
> Best regards,
> --
> Vishal Verma <vishal.l.verma@intel.com>
> 
> 

For the whole series :

Reviewed-by: Nikolay Borisov <nik.borisov@suse.com>