Re: [PATCH v2 4/9] x86/hyperv: Parse the ACPI wakeup mailbox

[Yunhong Jiang <yunhong.jiang@linux.intel.com>]

On Wed, Sep 04, 2024 at 02:56:49PM +0000, Michael Kelley wrote:
> From: Yunhong Jiang <yunhong.jiang@linux.intel.com> Sent: Tuesday, September 3, 2024 1:19 PM
> > 
> > On Mon, Sep 02, 2024 at 03:35:13AM +0000, Michael Kelley wrote:
> > > From: Yunhong Jiang <yunhong.jiang@linux.intel.com>
> > > >
> > > > Parse the wakeup mailbox VTL2 TDX guest. Put it to the guest_late_init, so
> > > > that it will be invoked before hyperv_init() where the mailbox address is
> > > > checked.
> > >
> > > Could you elaborate on the choice to set the wakeup_mailbox_address
> > > in ms_hyperv_late_init()? The code in hv_common.c is intended to be
> > > code that is architecture neutral (see the comment at the top of the module),
> > > so it's a red flag to see #ifdef CONFIG_X86_64. Couldn't the
> > > wakeup_mailbox_address be set in the x86 version of hyperv_init()
> > > before it is needed?
> > 
> > Sure, will try to put it in hyperv_init() before it's needed.
> > >
> > > >
> > > > Signed-off-by: Yunhong Jiang <yunhong.jiang@linux.intel.com>
> > > > ---
> > > >  arch/x86/include/asm/mshyperv.h | 3 +++
> > > >  arch/x86/kernel/cpu/mshyperv.c  | 2 ++
> > > >  drivers/hv/hv_common.c          | 8 ++++++++
> > > >  3 files changed, 13 insertions(+)
> > > >
> > > > diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> > > > index 390c4d13956d..5178b96c7fc9 100644
> > > > --- a/arch/x86/include/asm/mshyperv.h
> > > > +++ b/arch/x86/include/asm/mshyperv.h
> > > > @@ -10,6 +10,7 @@
> > > >  #include <asm/nospec-branch.h>
> > > >  #include <asm/paravirt.h>
> > > >  #include <asm/mshyperv.h>
> > > > +#include <asm/madt_wakeup.h>
> > > >
> > > >  /*
> > > >   * Hyper-V always provides a single IO-APIC at this MMIO address.
> > > > @@ -49,6 +50,8 @@ extern u64 hv_current_partition_id;
> > > >
> > > >  extern union hv_ghcb * __percpu *hv_ghcb_pg;
> > > >
> > > > +extern u64 wakeup_mailbox_addr;
> > > > +
> > > >  bool hv_isolation_type_snp(void);
> > > >  bool hv_isolation_type_tdx(void);
> > > >  u64 hv_tdx_hypercall(u64 control, u64 param1, u64 param2);
> > > > diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> > > > index 3d4237f27569..f6b727b4bd0b 100644
> > > > --- a/arch/x86/kernel/cpu/mshyperv.c
> > > > +++ b/arch/x86/kernel/cpu/mshyperv.c
> > > > @@ -43,6 +43,8 @@ struct ms_hyperv_info ms_hyperv;
> > > >  bool hyperv_paravisor_present __ro_after_init;
> > > >  EXPORT_SYMBOL_GPL(hyperv_paravisor_present);
> > > >
> > > > +u64 wakeup_mailbox_addr;
> > >
> > > This value duplicates acpi_mp_wake_mailbox_paddr in
> > > madt_wakeup.c. It looks like the duplicate value is used
> > > for two things:
> > >
> > > 1) In hv_is_private_mmio_tdx() to control the encrypted
> > > vs. decrypted mapping (Patch 5 of this series)
> > >
> > > 2) As a boolean in hv_vtl_early_init() to avoid overwriting
> > > the wakeup_secondary_cpu_64 value when
> > > dtb_parse_mp_wake() has set it to acpi_wakeup_cpu().
> > > (Patch 9 of this series).
> > >
> > > Having a duplicate value is messy, and I'm wondering if
> > > it can be avoided. For (1), hv_private_mmio_tdx() could call
> > > into a function added to madt_wakeup.c to make the
> > > check.  For (2), the check should probably be based on
> > > hv_isolation_type_tdx() instead of whether the wakeup
> > > mailbox address is set.  I'll note that Patch 5 of this series
> > > is using hv_isolation_type_tdx(), so there's a bit of an
> > > inconsistency in testing the wakeup_mailbox_addr in
> > > Patch 9.
> > 
> > I think your comment includes two points, the duplicated variables and the
> > incosistency in the testing.
> > 
> > Thank you for pointing out the duplication of wakeup_mailbox_addr with
> > acpi_mp_wake_mailbox_paddr. I didn't realize it. Yes, such duplication should be
> > avoided and will fix it in next submission.
> > 
> > Agree the inconsistency in testing wakeup_mailbox_addr and
> > hv_isolation_type_tdx() is not good. IMHO, the wakeup_mailbox_addr (or the new
> > function you proposed) is better than hv_isolation_type_tdx(), since the
> > wakeup_mailbox_addr is more directly related.  But hv_vtl_init_platform()
> > happens before DT parse, thus I have to use the hv_isolation_type_tdx() in it. I
> > don't have a good idea on how to fix this.
> > 
> > Thanks
> > --jyh
> > 
> 
> I don't think there's a requirement to set the "is_private_mmio"
> function in hv_vtl_init_platform(). It just needs to be set before
> acpi_wakeup_cpu() is called, which does the memremap() that will
> invoke the "is_private_mmio" function to decide whether to map
> as encrypted or decrypted.
> 
> So maybe setting the "is_private_mmio" function could be
> done after dtb_parse_mp_wake() is called in its new location, and
> you know you have a valid wake mailbox address? Again, I haven't
> worked out all the details, so this approach might be just as messy,
> but in a different way. Use your judgment ... :-)

Sorry that I didn't explain clearly. The testing in hv_vtl_init_platform() is
not only for the is_private_mmio, but also for the realmode_reserve(), which
happens before the DT parse.

BTW, I don't know why the trampoline_64.S is put into the real mode blob. I
don't find any specific requirement in the code, but I'm not sure if I missed
anything. If this dependency is removed, all the TDX guest will benefit.

Thank you
--jyh

> 
> Michael