On Mon, Jul 01, 2024 at 10:54:57AM +0100, Steven Price wrote: > Within a realm guest it's not possible for a device emulated by the VMM > to access arbitrary guest memory. So force the use of bounce buffers to > ensure that the memory the emulated devices are accessing is in memory > which is explicitly shared with the host. > > This adds a call to swiotlb_update_mem_attributes() which calls > set_memory_decrypted() to ensure the bounce buffer memory is shared with > the host. For non-realm guests or hosts this is a no-op. > > Co-developed-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx> > Signed-off-by: Steven Price <steven.price@xxxxxxx> > --- > v3: Simplify mem_init() by using a 'flags' variable. > --- > arch/arm64/kernel/rsi.c | 2 ++ > arch/arm64/mm/init.c | 10 +++++++++- > 2 files changed, 11 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kernel/rsi.c b/arch/arm64/kernel/rsi.c > index 7ac5fc4a27d0..918db258cd4a 100644 > --- a/arch/arm64/kernel/rsi.c > +++ b/arch/arm64/kernel/rsi.c > @@ -6,6 +6,8 @@ > #include <linux/jump_label.h> > #include <linux/memblock.h> > #include <linux/psci.h> > +#include <linux/swiotlb.h> > + > #include <asm/rsi.h> > > struct realm_config config; > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c > index 9b5ab6818f7f..1d595b63da71 100644 > --- a/arch/arm64/mm/init.c > +++ b/arch/arm64/mm/init.c > @@ -41,6 +41,7 @@ > #include <asm/kvm_host.h> > #include <asm/memory.h> > #include <asm/numa.h> > +#include <asm/rsi.h> > #include <asm/sections.h> > #include <asm/setup.h> > #include <linux/sizes.h> > @@ -369,8 +370,14 @@ void __init bootmem_init(void) > */ > void __init mem_init(void) > { > + unsigned int flags = SWIOTLB_VERBOSE; > bool swiotlb = max_pfn > PFN_DOWN(arm64_dma_phys_limit); > > + if (is_realm_world()) { > + swiotlb = true; > + flags |= SWIOTLB_FORCE; > + } > + > if (IS_ENABLED(CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC) && !swiotlb) { > /* > * If no bouncing needed for ZONE_DMA, reduce the swiotlb > @@ -382,7 +389,8 @@ void __init mem_init(void) > swiotlb = true; > } > > - swiotlb_init(swiotlb, SWIOTLB_VERBOSE); > + swiotlb_init(swiotlb, flags); > + swiotlb_update_mem_attributes(); Why do we have to call this so early? Certainly, we won't have probed the hypercalls under pKVM yet and I think it would be a lot cleaner if you could defer your RSI discovery too. Looking forward to the possibility of device assignment in future, how do you see DMA_BOUNCE_UNALIGNED_KMALLOC interacting with a decrypted SWIOTLB buffer? I'm struggling to wrap my head around how to fix that properly. Will