Re: [PATCH v6 09/16] KVM: TDX: Pass desired page level in err code for page fault handler

Isaku Yamahata
2023-11-21T10:27:34Z

On Mon, Nov 20, 2023 at 07:24:51PM +0800,
Binbin Wu <binbin.wu@linux.intel.com> wrote:

>
>
> On 11/7/2023 11:00 PM, isaku.yamahata@intel.com wrote:
> > From: Xiaoyao Li <xiaoyao.li@intel.com>
> >
> > For TDX, EPT violation can happen when TDG.MEM.PAGE.ACCEPT.
> > And TDG.MEM.PAGE.ACCEPT contains the desired accept page level of TD guest.
> >
> > 1. KVM can map it with 4KB page while TD guest wants to accept 2MB page.
> >
> > TD geust will get TDX_PAGE_SIZE_MISMATCH and it should try to accept
> > 4KB size.
> >
> > 2. KVM can map it with 2MB page while TD guest wants to accept 4KB page.
> >
> > KVM needs to honor it because
> > a) there is no way to tell guest KVM maps it as 2MB size. And
> > b) guest accepts it in 4KB size since guest knows some other 4KB page
> > in the same 2MB range will be used as shared page.
> >
> > For case 2, it need to pass desired page level to MMU's
> > page_fault_handler. Use bit 29:31 of kvm PF error code for this purpose.
> The shortlog is the same as patch 7/16..., I am a bit confused by the
> structure of this patch series...
> Can this patch be squashed into 7/16?

Patch 7 should include the changes to arch/x86/include/asm/kvm_host.h and
arch/x86/kvm/mmu/mmu.c. and use PFERR_LEVEL().
Patch 9 should include the changes arch/x86/kvm/vmx/*.

I'll fix them.

> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index eed36c1eedb7..c16823f3326e 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -285,6 +285,8 @@ enum x86_intercept_stage;
> > PFERR_WRITE_MASK | \
> > PFERR_PRESENT_MASK)
> > +#define PFERR_LEVEL(err_code) (((err_code) & PFERR_LEVEL_MASK) >> PFERR_LEVEL_START_BIT)
> It's defined, but never used?

I'll make kvm_tdp_page_fault() use it.

> > diff --git a/arch/x86/kvm/vmx/tdx_arch.h b/arch/x86/kvm/vmx/tdx_arch.h
> > index 9f93250d22b9..ba41fefa47ee 100644
> > --- a/arch/x86/kvm/vmx/tdx_arch.h
> > +++ b/arch/x86/kvm/vmx/tdx_arch.h
> > @@ -218,4 +218,23 @@ union tdx_sept_level_state {
> > u64 raw;
> > };
> > +union tdx_ext_exit_qualification {
> > + struct {
> > + u64 type : 4;
> > + u64 reserved0 : 28;
> > + u64 req_sept_level : 3;
> > + u64 err_sept_level : 3;
> > + u64 err_sept_state : 8;
> > + u64 err_sept_is_leaf : 1;
> > + u64 reserved1 : 17;
> > + };
> > + u64 full;
> > +};
> > +
> > +enum tdx_ext_exit_qualification_type {
> > + EXT_EXIT_QUAL_NONE = 0,
> > + EXT_EXIT_QUAL_ACCEPT,
> Since this value should be fixed to 1, maybe better to initialize it to 1
> for future proof?

ok.
--
Isaku Yamahata <isaku.yamahata@linux.intel.com>