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SubjectRe: [RFC v1 22/26] x86/tdx: Exclude Shared bit from __PHYSICAL_MASK
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On 2/5/21 3:38 PM, Kuppuswamy Sathyanarayanan wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
>
> tdx_shared_mask() returns the mask that has to be set in page table
> entry to make page shared with VMM.

Needs to be either:

has to be set in a page table entry
or
has to be set in page table entries

Pick one, please. But, the grammar is wrong as-is.


> index 8fa654d61ac2..f10a00c4ad7f 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -875,6 +875,7 @@ config INTEL_TDX_GUEST
> select PARAVIRT_XL
> select X86_X2APIC
> select SECURITY_LOCKDOWN_LSM
> + select X86_MEM_ENCRYPT_COMMON
> help
> Provide support for running in a trusted domain on Intel processors
> equipped with Trusted Domain eXtenstions. TDX is an new Intel
> diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
> index b46ae140e39b..9bbfe6520ea4 100644
> --- a/arch/x86/include/asm/tdx.h
> +++ b/arch/x86/include/asm/tdx.h
> @@ -104,5 +104,6 @@ long tdx_kvm_hypercall3(unsigned int nr, unsigned long p1, unsigned long p2,
> long tdx_kvm_hypercall4(unsigned int nr, unsigned long p1, unsigned long p2,
> unsigned long p3, unsigned long p4);
>
> +phys_addr_t tdx_shared_mask(void);

I know it's redundant, but extern this, please. Ditto for all the other
declarations in that header.

> #endif
> #endif /* _ASM_X86_TDX_H */
> diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
> index ae37498df981..9681f4a0b4e0 100644
> --- a/arch/x86/kernel/tdx.c
> +++ b/arch/x86/kernel/tdx.c
> @@ -41,6 +41,11 @@ bool is_tdx_guest(void)
> }
> EXPORT_SYMBOL_GPL(is_tdx_guest);
>
> +phys_addr_t tdx_shared_mask(void)
> +{
> + return 1ULL << (td_info.gpa_width - 1);
> +}

A comment would be helpful:

/* The highest bit of a guest physical address is the "sharing" bit */

> static void tdx_get_info(void)
> {
> register long rcx asm("rcx");
> @@ -56,6 +61,9 @@ static void tdx_get_info(void)
>
> td_info.gpa_width = rcx & GENMASK(5, 0);
> td_info.attributes = rdx;
> +
> + /* Exclude Shared bit from the __PHYSICAL_MASK */
> + physical_mask &= ~tdx_shared_mask();
> }

I wish we had all of these 'physical_mask' manipulations in a single
spot. Can we consolidate these instead of having TDX and SME poke at
them individually?

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