Re: [RFC PATCH V5 11/15] x86/sev: Add a #HV exception handler

[Gupta, Pankaj]

On 5/5/2023 12:59 PM, Gupta, Pankaj wrote:
> Hi Tianyu,
>
> I tried to understand some details of this patch. Please find below
> some comments/questions.
>
> Thanks,
>
>
> > Add a #HV exception handler that uses IST stack.
> >
> > Signed-off-by: Tianyu Lan <tiala@xxxxxxxxxxxxx>
> > ---
> > Change since RFC V2:
> >         * Remove unnecessary line in the change log.
> > ---
> >   arch/x86/entry/entry_64.S             | 22 +++++++----
> >   arch/x86/include/asm/cpu_entry_area.h |  6 +++
> >   arch/x86/include/asm/idtentry.h       | 40 +++++++++++++++++++-
> >   arch/x86/include/asm/page_64_types.h  |  1 +
> >   arch/x86/include/asm/trapnr.h         |  1 +
> >   arch/x86/include/asm/traps.h          |  1 +
> >   arch/x86/kernel/cpu/common.c          |  1 +
> >   arch/x86/kernel/dumpstack_64.c        |  9 ++++-
> >   arch/x86/kernel/idt.c                 |  1 +
> >   arch/x86/kernel/sev.c                 | 53 +++++++++++++++++++++++++++
> >   arch/x86/kernel/traps.c               | 40 ++++++++++++++++++++
> >   arch/x86/mm/cpu_entry_area.c          |  2 +
> >   12 files changed, 165 insertions(+), 12 deletions(-)
> >
> > diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> > index eccc3431e515..653b1f10699b 100644
> > --- a/arch/x86/entry/entry_64.S
> > +++ b/arch/x86/entry/entry_64.S
> > @@ -496,7 +496,7 @@ SYM_CODE_END(\asmsym)
> >   #ifdef CONFIG_AMD_MEM_ENCRYPT
> >   /**
> > - * idtentry_vc - Macro to generate entry stub for #VC
> > + * idtentry_sev - Macro to generate entry stub for #VC
> >    * @vector:        Vector number
> >    * @asmsym:        ASM symbol for the entry point
> >    * @cfunc:        C function to be called
> > @@ -515,14 +515,18 @@ SYM_CODE_END(\asmsym)
> >    *
> >    * The macro is only used for one vector, but it is planned to be 
> > extended in
> >    * the future for the #HV exception.
> > - */
> > -.macro idtentry_vc vector asmsym cfunc
> > +*/
> > +.macro idtentry_sev vector asmsym cfunc has_error_code:req
> >   SYM_CODE_START(\asmsym)
> >       UNWIND_HINT_IRET_REGS
> >       ENDBR
> >       ASM_CLAC
> >       cld
> > +    .if \vector == X86_TRAP_HV
> > +        pushq    $-1            /* ORIG_RAX: no syscall */
> > +    .endif
> > +
> >       /*
> >        * If the entry is from userspace, switch stacks and treat it as
> >        * a normal entry.
> > @@ -545,7 +549,12 @@ SYM_CODE_START(\asmsym)
> >        * stack.
> >        */
> >       movq    %rsp, %rdi        /* pt_regs pointer */
> > -    call    vc_switch_off_ist
> > +    .if \vector == X86_TRAP_VC
> > +        call    vc_switch_off_ist
>
> I think the stack switching logic is similar for #VC & #HV.
> So, we can use common function. Just the corresponding fallback
> stack switching is different. Maybe we can pass the hint as an
> argument (%rsi?) to something like "sev_switch_off_ist()", and use
> the corresponding (#HV or #VC) fallbacks stack?

Also, Please include the below patch from Ashish for #HV
reentrancy check.

https://github.com/ashkalra/linux/commit/6975484094b7cb8d703c45066780dd85043cd040

Thanks,
Pankaj