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Re: [Resend RFC PATCH V4 09/13] x86/Swiotlb/HV: Add Swiotlb bounce buffer remap function for HV IVM

Thanks for review.

On 7/20/2021 9:54 PM, Christoph Hellwig wrote:

Please split the swiotlb changes into a separate patch from the

OK. Will update.

+ * hv_map_memory - map memory to extra space in the AMD SEV-SNP Isolation VM.
+ */
+unsigned long hv_map_memory(unsigned long addr, unsigned long size)
+       unsigned long *pfns = kcalloc(size / HV_HYP_PAGE_SIZE,
+                                     sizeof(unsigned long),
+                      GFP_KERNEL);
+       unsigned long vaddr;
+       int i;
+       if (!pfns)
+               return (unsigned long)NULL;
+       for (i = 0; i < size / HV_HYP_PAGE_SIZE; i++)
+               pfns[i] = virt_to_hvpfn((void *)addr + i * HV_HYP_PAGE_SIZE) +
+                       (ms_hyperv.shared_gpa_boundary >> HV_HYP_PAGE_SHIFT);
+       vaddr = (unsigned long)vmap_pfn(pfns, size / HV_HYP_PAGE_SIZE,
+                                       PAGE_KERNEL_IO);
+       kfree(pfns);
+       return vaddr;

This seems to miss a 'select VMAP_PFN'.

VMAP_PFN has been selected in the previous patch "RFC PATCH V4 08/13]
HV/Vmbus: Initialize VMbus ring buffer for Isolation VM"

But more importantly I don't
think this actually works.  Various DMA APIs do expect a struct page
backing, so how is this going to work with say dma_mmap_attrs or

dma_mmap_attrs() and dma_get_sgtable_attrs() get input virtual address
belonging to backing memory with struct page and returns bounce buffer
dma physical address which is below shared_gpa_boundary(vTOM) and passed
to Hyper-V via vmbus protocol.

The new map virtual address is only to access bounce buffer in swiotlb
code and will not be used other places. It's stored in the mem->vstart.
So the new API set_memory_decrypted_map() in this series is only called
in the swiotlb code. Other platforms may replace set_memory_decrypted()
with set_memory_decrypted_map() as requested.

+static unsigned long __map_memory(unsigned long addr, unsigned long size)
+       if (hv_is_isolation_supported())
+               return hv_map_memory(addr, size);
+       return addr;
+static void __unmap_memory(unsigned long addr)
+       if (hv_is_isolation_supported())
+               hv_unmap_memory(addr);
+unsigned long set_memory_decrypted_map(unsigned long addr, unsigned long size)
+       if (__set_memory_enc_dec(addr, size / PAGE_SIZE, false))
+               return (unsigned long)NULL;
+       return __map_memory(addr, size);
+int set_memory_encrypted_unmap(unsigned long addr, unsigned long size)
+       __unmap_memory(addr);
+       return __set_memory_enc_dec(addr, size / PAGE_SIZE, true);

Why this obsfucation into all kinds of strange helpers?  Also I think
we want an ops vectors (or alternative calls) instead of the random
if checks here.

Yes, agree and will add ops for different platforms to map/unmap memory.

+ * @vstart:    The virtual start address of the swiotlb memory pool. The 
+ *             memory pool may be remapped in the memory encrypted case and 

Normall we'd call this vaddr or cpu_addr.

OK. Will update.

-       set_memory_decrypted((unsigned long)vaddr, bytes >> PAGE_SHIFT);
-       memset(vaddr, 0, bytes);
+       mem->vstart = (void *)set_memory_decrypted_map((unsigned long)vaddr, 

Please always pass kernel virtual addresses as pointers.

And I think these APIs might need better names, e.g.

arch_dma_map_decrypted and arch_dma_unmap_decrypted.

Also these will need fallback versions for non-x86 architectures that
currently use memory encryption.

Sure. Will update in the next version.



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