Messages in this thread | | | Date | Tue, 6 Apr 2021 18:37:55 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [RFC v1 21/26] x86/mm: Move force_dma_unencrypted() to common code |
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On Thu, Apr 01, 2021 at 01:06:29PM -0700, Dave Hansen wrote: > On 2/5/21 3:38 PM, Kuppuswamy Sathyanarayanan wrote: > > From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> > > > > Intel TDX doesn't allow VMM to access guest memory. Any memory that is > > required for communication with VMM suppose to be shared explicitly by > > s/suppose to/must/
Right.
> > setting the bit in page table entry. The shared memory is similar to > > unencrypted memory in AMD SME/SEV terminology. > > In addition to setting the page table bit, there's also a dance to go > through to convert the memory. Please mention the procedure here at > least. It's very different from SME.
" After setting the shared bit, the conversion must be completed with MapGPA TDVMALL. The call informs VMM about the conversion and makes it remove the GPA from the S-EPT mapping. "
> > force_dma_unencrypted() has to return true for TDX guest. Move it out of > > AMD SME code. > > You lost me here. What does force_dma_unencrypted() have to do with > host/guest shared memory?
" AMD SEV makes force_dma_unencrypted() return true which triggers set_memory_decrypted() calls on all DMA allocations. TDX will use the same code path to make DMA allocations shared. "
> > Introduce new config option X86_MEM_ENCRYPT_COMMON that has to be > > selected by all x86 memory encryption features. > > Please also mention what will set it. I assume TDX guest support will > set this option. It's probably also worth a sentence to say that > force_dma_unencrypted() will have TDX-specific code added to it. (It > will, right??)
" Only AMD_MEM_ENCRYPT uses the option now. TDX will be the second one. "
> > This is preparation for TDX changes in DMA code. > > Probably best to also mention that this effectively just moves code > around. This patch should have no functional changes at runtime.
Isn't it what the subject says? :P
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > > index 0374d9f262a5..8fa654d61ac2 100644 > > --- a/arch/x86/Kconfig > > +++ b/arch/x86/Kconfig > > @@ -1538,14 +1538,18 @@ config X86_CPA_STATISTICS > > helps to determine the effectiveness of preserving large and huge > > page mappings when mapping protections are changed. > > > > +config X86_MEM_ENCRYPT_COMMON > > + select ARCH_HAS_FORCE_DMA_UNENCRYPTED > > + select DYNAMIC_PHYSICAL_MASK > > + def_bool n > > + > > config AMD_MEM_ENCRYPT > > bool "AMD Secure Memory Encryption (SME) support" > > depends on X86_64 && CPU_SUP_AMD > > select DMA_COHERENT_POOL > > - select DYNAMIC_PHYSICAL_MASK > > select ARCH_USE_MEMREMAP_PROT > > - select ARCH_HAS_FORCE_DMA_UNENCRYPTED > > select INSTRUCTION_DECODER > > + select X86_MEM_ENCRYPT_COMMON > > help > > Say yes to enable support for the encryption of system memory. > > This requires an AMD processor that supports Secure Memory > > diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h > > index 30a3b30395ad..95e534cffa99 100644 > > --- a/arch/x86/include/asm/io.h > > +++ b/arch/x86/include/asm/io.h > > @@ -257,10 +257,12 @@ static inline void slow_down_io(void) > > > > #endif > > > > -#ifdef CONFIG_AMD_MEM_ENCRYPT > > #include <linux/jump_label.h> > > > > extern struct static_key_false sev_enable_key; > > This _looks_ odd. sev_enable_key went from being under > CONFIG_AMD_MEM_ENCRYPT to being unconditionally referenced.
Not referenced, but declared.
> Could you explain a bit more? > > I would have expected it tot at *least* be tied to the new #ifdef.
Looks like a fixup got folded into a wrong patch. It supposed to be in "x86/kvm: Use bounce buffers for TD guest".
This declaration allows to get away without any #ifdefs in mem_encrypt_init() when !CONFIG_AMD_MEM_ENCRYPT: sev_active() is false at compile-time and sev_enable_key never referenced.
Sathya, could move it to the right patch?
> > +#ifdef CONFIG_AMD_MEM_ENCRYPT > > + > > static inline bool sev_key_active(void) > > { > > return static_branch_unlikely(&sev_enable_key); > > diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile > > index 5864219221ca..b31cb52bf1bd 100644 > > --- a/arch/x86/mm/Makefile > ...
-- Kirill A. Shutemov
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