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

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Message-ID: <20231121102723.GG1109547@ls.amr.corp.intel.com>
Date:   Tue, 21 Nov 2023 02:27:23 -0800
From:   Isaku Yamahata <isaku.yamahata@...ux.intel.com>
To:     Binbin Wu <binbin.wu@...ux.intel.com>
Cc:     isaku.yamahata@...el.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
        Paolo Bonzini <pbonzini@...hat.com>, erdemaktas@...gle.com,
        Sean Christopherson <seanjc@...gle.com>,
        Sagi Shahar <sagis@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Kai Huang <kai.huang@...el.com>,
        Zhi Wang <zhi.wang.linux@...il.com>, chen.bo@...el.com,
        hang.yuan@...el.com, tina.zhang@...el.com,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        isaku.yamahata@...ux.intel.com
Subject: Re: [PATCH v6 09/16] KVM: TDX: Pass desired page level in err code
 for page fault handler

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

> 
> 
> On 11/7/2023 11:00 PM, isaku.yamahata@...el.com wrote:
> > From: Xiaoyao Li <xiaoyao.li@...el.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@...ux.intel.com>