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a="186271182" X-IronPort-AV: E=Sophos;i="5.82,282,1613462400"; d="scan'208";a="186271182" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 07 May 2021 14:36:34 -0700 IronPort-SDR: ErWaAtH1tOhxtc0GAH4hrpHzPMBjBmij7NxB6d2/So/2wERRiPQ/oAy3dEqLjbXK8tcTAfu7Ms 3qOr7d4CZHjA== X-IronPort-AV: E=Sophos;i="5.82,282,1613462400"; d="scan'208";a="431675842" Received: from msandrid-mobl.amr.corp.intel.com (HELO [10.212.134.124]) ([10.212.134.124]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 07 May 2021 14:36:33 -0700 Subject: Re: [RFC v2 08/32] x86/traps: Add #VE support for TDX guest To: Kuppuswamy Sathyanarayanan , Peter Zijlstra , Andy Lutomirski , Dan Williams , Tony Luck Cc: Andi Kleen , Kirill Shutemov , Kuppuswamy Sathyanarayanan , Raj Ashok , Sean Christopherson , linux-kernel@vger.kernel.org, Sean Christopherson References: <8a1d6930f784cb57c957cf20cea870947db91e05.1619458733.git.sathyanarayanan.kuppuswamy@linux.intel.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <8a1d6930f784cb57c957cf20cea870947db91e05.1619458733.git.sathyanarayanan.kuppuswamy@linux.intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/26/21 11:01 AM, Kuppuswamy Sathyanarayanan wrote: ... > The #VE cannot be nested before TDGETVEINFO is called, if there is any > reason for it to nest the TD would shut down. The TDX module guarantees > that no NMIs (or #MC or similar) can happen in this window. After > TDGETVEINFO the #VE handler can nest if needed, although we don’t expect > it to happen normally. I think this description really needs some work. Does "The #VE cannot be nested" mean that "hardware guarantees that #VE will not be generated", or "the #VE must not be nested"? What does "the TD would shut down" mean? I think you mean that instead of delivering a nested #VE the hardware would actually exit to the host and TDX would prevent the guest from being reentered. Right? > diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h > index 5eb3bdf36a41..41a0732d5f68 100644 > --- a/arch/x86/include/asm/idtentry.h > +++ b/arch/x86/include/asm/idtentry.h > @@ -619,6 +619,10 @@ DECLARE_IDTENTRY_XENCB(X86_TRAP_OTHER, exc_xen_hypervisor_callback); > DECLARE_IDTENTRY_RAW(X86_TRAP_OTHER, exc_xen_unknown_trap); > #endif > > +#ifdef CONFIG_INTEL_TDX_GUEST > +DECLARE_IDTENTRY(X86_TRAP_VE, exc_virtualization_exception); > +#endif > + > /* Device interrupts common/spurious */ > DECLARE_IDTENTRY_IRQ(X86_TRAP_OTHER, common_interrupt); > #ifdef CONFIG_X86_LOCAL_APIC > diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h > index c5a870cef0ae..1ca55d8e9963 100644 > --- a/arch/x86/include/asm/tdx.h > +++ b/arch/x86/include/asm/tdx.h > @@ -11,6 +11,7 @@ > #include > > #define TDINFO 1 > +#define TDGETVEINFO 3 > > struct tdcall_output { > u64 rcx; > @@ -29,6 +30,20 @@ struct tdvmcall_output { > u64 r15; > }; > > +struct ve_info { > + u64 exit_reason; > + u64 exit_qual; > + u64 gla; > + u64 gpa; > + u32 instr_len; > + u32 instr_info; > +}; Is this an architectural structure or some software construct? > +unsigned long tdg_get_ve_info(struct ve_info *ve); > + > +int tdg_handle_virtualization_exception(struct pt_regs *regs, > + struct ve_info *ve); > + > /* Common API to check TDX support in decompression and common kernel code. */ > bool is_tdx_guest(void); > > diff --git a/arch/x86/kernel/idt.c b/arch/x86/kernel/idt.c > index ee1a283f8e96..546b6b636c7d 100644 > --- a/arch/x86/kernel/idt.c > +++ b/arch/x86/kernel/idt.c > @@ -64,6 +64,9 @@ static const __initconst struct idt_data early_idts[] = { > */ > INTG(X86_TRAP_PF, asm_exc_page_fault), > #endif > +#ifdef CONFIG_INTEL_TDX_GUEST > + INTG(X86_TRAP_VE, asm_exc_virtualization_exception), > +#endif > }; > > /* > @@ -87,6 +90,9 @@ static const __initconst struct idt_data def_idts[] = { > INTG(X86_TRAP_MF, asm_exc_coprocessor_error), > INTG(X86_TRAP_AC, asm_exc_alignment_check), > INTG(X86_TRAP_XF, asm_exc_simd_coprocessor_error), > +#ifdef CONFIG_INTEL_TDX_GUEST > + INTG(X86_TRAP_VE, asm_exc_virtualization_exception), > +#endif > > #ifdef CONFIG_X86_32 > TSKG(X86_TRAP_DF, GDT_ENTRY_DOUBLEFAULT_TSS), > diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c > index b63275db1db9..ccfcb07bfb2c 100644 > --- a/arch/x86/kernel/tdx.c > +++ b/arch/x86/kernel/tdx.c > @@ -82,6 +82,44 @@ static void tdg_get_info(void) > td_info.attributes = out.rdx; > } > > +unsigned long tdg_get_ve_info(struct ve_info *ve) > +{ > + u64 ret; > + struct tdcall_output out = {0}; > + > + /* > + * The #VE cannot be nested before TDGETVEINFO is called, > + * if there is any reason for it to nest the TD would shut > + * down. The TDX module guarantees that no NMIs (or #MC or > + * similar) can happen in this window. After TDGETVEINFO > + * the #VE handler can nest if needed, although we don’t > + * expect it to happen normally. > + */ I find that description a bit unsatisfying. Could we make this a bit more concrete? By the way, what about *normal* interrupts? Maybe we should talk about this in terms of *rules* that folks need to follow. Maybe: NMIs and machine checks are suppressed. Before this point any #VE is fatal. After this point, NMIs and additional #VEs are permitted. > + ret = __tdcall(TDGETVEINFO, 0, 0, 0, 0, &out); > + > + ve->exit_reason = out.rcx; > + ve->exit_qual = out.rdx; > + ve->gla = out.r8; > + ve->gpa = out.r9; > + ve->instr_len = out.r10 & UINT_MAX; > + ve->instr_info = out.r10 >> 32; > + > + return ret; > +} > + > +int tdg_handle_virtualization_exception(struct pt_regs *regs, > + struct ve_info *ve) > +{ > + /* > + * TODO: Add handler support for various #VE exit > + * reasons. It will be added by other patches in > + * the series. > + */ > + pr_warn("Unexpected #VE: %lld\n", ve->exit_reason); > + return -EFAULT; > +} > + > void __init tdx_early_init(void) > { > if (!cpuid_has_tdx_guest()) > diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c > index 213d4aa8e337..64869aa88a5a 100644 > --- a/arch/x86/kernel/traps.c > +++ b/arch/x86/kernel/traps.c > @@ -61,6 +61,7 @@ > #include > #include > #include > +#include > > #ifdef CONFIG_X86_64 > #include > @@ -1140,6 +1141,35 @@ DEFINE_IDTENTRY(exc_device_not_available) > } > } > > +#ifdef CONFIG_INTEL_TDX_GUEST > +DEFINE_IDTENTRY(exc_virtualization_exception) > +{ > + struct ve_info ve; > + int ret; > + > + RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); > + > + /* > + * Consume #VE info before re-enabling interrupts. It will be > + * re-enabled after executing the TDGETVEINFO TDCALL. > + */ "It" is nebulous here. Is this talking about NMIs, or the cond_local_irq_enable() that is "after" TDGETVEINFO? > + ret = tdg_get_ve_info(&ve); > + > + cond_local_irq_enable(regs); > + > + if (!ret) > + ret = tdg_handle_virtualization_exception(regs, &ve); > + /* > + * If tdg_handle_virtualization_exception() could not process > + * it successfully, treat it as #GP(0) and handle it. > + */ > + if (ret) > + do_general_protection(regs, 0); > + > + cond_local_irq_disable(regs); > +} > +#endif > + > #ifdef CONFIG_X86_32 > DEFINE_IDTENTRY_SW(iret_error) > { >