On 28/7/25 20:03, Jason Gunthorpe wrote:
On Mon, Jul 28, 2025 at 07:21:41PM +0530, Aneesh Kumar K.V (Arm) wrote:
@@ -48,3 +49,12 @@ int set_memory_decrypted(unsigned long addr, int numpages)
return crypt_ops->decrypt(addr, numpages);
}
EXPORT_SYMBOL_GPL(set_memory_decrypted);
+
+bool force_dma_unencrypted(struct device *dev)
+{
+ if (dev->tdi_enabled)
+ return false;
Is this OK? I see code like this:
static inline dma_addr_t phys_to_dma_direct(struct device *dev,
phys_addr_t phys)
{
if (force_dma_unencrypted(dev))
return phys_to_dma_unencrypted(dev, phys);
return phys_to_dma(dev, phys);
I did write this in the first place so I'll comment :)
What are the ARM rules for generating dma addreses?
1) Device is T=0, memory is unencrypted, call dma_addr_unencrypted()
and do "top bit IBA set"
2) Device is T=1, memory is encrypted, use the phys_to_dma() normally
3) Device it T=1, memory is uncrypted, use the phys_to_dma()
normally??? Seems odd, I would have guessed the DMA address sould
be the same as case #1?
Can you document this in a comment?
On AMD, T=1 only encrypts the PCIe trafic, when a DMA request hits the IOMMU, the IOMMU decrypts it and then decides whether to encrypt it with a memory key: if there is secure vIOMMU - it will do what Cbit says in the guest IOMMU table (this is in the works) oooor just always set Cbit without guest vIOMMU (which is a big knob per a device and this is what my patches do now).
And with vIOMMU, I'd expect phys_to_dma_direct() not to be called as this one is in a direct map path.
diff --git a/include/linux/device.h b/include/linux/device.h
index 4940db137fff..d62e0dd9d8ee 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -688,6 +688,7 @@ struct device {
#ifdef CONFIG_IOMMU_DMA
bool dma_iommu:1;
#endif
+ bool tdi_enabled:1;
};
I would give the dev->tdi_enabled a clearer name, maybe
dev->encrypted_dma_supported ?
May be but "_enabled", not "_supported". And, ideally, with vIOMMU, at least AMD won't be needing it.
Also need to think carefully of a bitfield is OK here, we can't
locklessly change a bitfield so need to audit that all members are set
under, probably, the device lock or some other single threaded hand
waving. It seems believable it is like that but should be checked out,
and add a lockdep if it relies on the device lock.
True.
Jason
--
Alexey
