Re: [PATCH v5 07/16] x86/kvm: Use bounce buffers for TD guest

[Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@linux.intel.com>]

On 10/20/21 9:39 AM, Tom Lendacky wrote:
> On 10/8/21 7:37 PM, Kuppuswamy Sathyanarayanan wrote:
>> From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
>>
>> Intel TDX doesn't allow VMM to directly access guest private memory.
>> Any memory that is required for communication with VMM must be shared
>> explicitly. The same rule applies for any DMA to and from TDX guest.
>> All DMA pages had to marked as shared pages. A generic way to achieve
>> this without any changes to device drivers is to use the SWIOTLB
>> framework.
>>
>> This method of handling is similar to AMD SEV. So extend this support
>> for TDX guest as well. Also since there are some common code between
>> AMD SEV and TDX guest in mem_encrypt_init(), move it to
>> mem_encrypt_common.c and call AMD specific init function from it
>>
>> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
>> Reviewed-by: Andi Kleen <ak@linux.intel.com>
>> Reviewed-by: Tony Luck <tony.luck@intel.com>
>> Signed-off-by: Kuppuswamy Sathyanarayanan 
>> <sathyanarayanan.kuppuswamy@linux.intel.com>
>> ---
>>
>> Changes since v4:
>>   * Replaced prot_guest_has() with cc_guest_has().
>>
>> Changes since v3:
>>   * Rebased on top of Tom Lendacky's protected guest
>>     changes (https://lore.kernel.org/patchwork/cover/1468760/)
>>
>> Changes since v1:
>>   * Removed sme_me_mask check for amd_mem_encrypt_init() in 
>> mem_encrypt_init().
>>
>>   arch/x86/include/asm/mem_encrypt_common.h |  3 +++
>>   arch/x86/kernel/tdx.c                     |  2 ++
>>   arch/x86/mm/mem_encrypt.c                 |  5 +----
>>   arch/x86/mm/mem_encrypt_common.c          | 14 ++++++++++++++
>>   4 files changed, 20 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/mem_encrypt_common.h 
>> b/arch/x86/include/asm/mem_encrypt_common.h
>> index 697bc40a4e3d..bc90e565bce4 100644
>> --- a/arch/x86/include/asm/mem_encrypt_common.h
>> +++ b/arch/x86/include/asm/mem_encrypt_common.h
>> @@ -8,11 +8,14 @@
>>   #ifdef CONFIG_AMD_MEM_ENCRYPT
>>   bool amd_force_dma_unencrypted(struct device *dev);
>> +void __init amd_mem_encrypt_init(void);
>>   #else /* CONFIG_AMD_MEM_ENCRYPT */
>>   static inline bool amd_force_dma_unencrypted(struct device *dev)
>>   {
>>       return false;
>>   }
>> +
>> +static inline void amd_mem_encrypt_init(void) {}
>>   #endif /* CONFIG_AMD_MEM_ENCRYPT */
>>   #endif
>> diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
>> index 433f366ca25c..ce8e3019b812 100644
>> --- a/arch/x86/kernel/tdx.c
>> +++ b/arch/x86/kernel/tdx.c
>> @@ -12,6 +12,7 @@
>>   #include <asm/insn.h>
>>   #include <asm/insn-eval.h>
>>   #include <linux/sched/signal.h> /* force_sig_fault() */
>> +#include <linux/swiotlb.h>
>>   /* TDX Module call Leaf IDs */
>>   #define TDX_GET_INFO            1
>> @@ -577,6 +578,7 @@ void __init tdx_early_init(void)
>>       pv_ops.irq.halt = tdx_halt;
>>       legacy_pic = &null_legacy_pic;
>> +    swiotlb_force = SWIOTLB_FORCE;
>>       cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "tdx:cpu_hotplug",
>>                 NULL, tdx_cpu_offline_prepare);
>> diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
>> index 5d7fbed73949..8385bc4565e9 100644
>> --- a/arch/x86/mm/mem_encrypt.c
>> +++ b/arch/x86/mm/mem_encrypt.c
>> @@ -438,14 +438,11 @@ static void print_mem_encrypt_feature_info(void)
>>   }
>>   /* Architecture __weak replacement functions */
>> -void __init mem_encrypt_init(void)
>> +void __init amd_mem_encrypt_init(void)
>>   {
>>       if (!sme_me_mask)
>>           return;
>> -    /* Call into SWIOTLB to update the SWIOTLB DMA buffers */
>> -    swiotlb_update_mem_attributes();
>> -
>>       /*
>>        * With SEV, we need to unroll the rep string I/O instructions,
>>        * but SEV-ES supports them through the #VC handler.
>> diff --git a/arch/x86/mm/mem_encrypt_common.c 
>> b/arch/x86/mm/mem_encrypt_common.c
>> index 119a9056efbb..6fe44c6cb753 100644
>> --- a/arch/x86/mm/mem_encrypt_common.c
>> +++ b/arch/x86/mm/mem_encrypt_common.c
>> @@ -10,6 +10,7 @@
>>   #include <asm/mem_encrypt_common.h>
>>   #include <linux/dma-mapping.h>
>>   #include <linux/cc_platform.h>
>> +#include <linux/swiotlb.h>
>>   /* Override for DMA direct allocation check - 
>> ARCH_HAS_FORCE_DMA_UNENCRYPTED */
>>   bool force_dma_unencrypted(struct device *dev)
>> @@ -24,3 +25,16 @@ bool force_dma_unencrypted(struct device *dev)
>>       return false;
>>   }
>> +
>> +/* Architecture __weak replacement functions */
>> +void __init mem_encrypt_init(void)
>> +{
>> +    /*
>> +     * For TDX guest or SEV/SME, call into SWIOTLB to update
>> +     * the SWIOTLB DMA buffers
>> +     */
>> +    if (sme_me_mask || cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT))
> 
> Can't you just make this:
> 
>      if (cc_platform_has(CC_ATTR_MEM_ENCRYPT))
> 
> SEV will return true if sme_me_mask is not zero and TDX should only 
> return true if it is TDX guest, right?

Yes. It can be simplified.

But where shall we leave this function cc_platform.c or here?

> 
> Thanks,
> Tom
> 
>> +        swiotlb_update_mem_attributes();
>> +
>> +    amd_mem_encrypt_init();
>> +}
>>

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer