[PATCH v2 06/12] swiotlb: Remove bounce buffer remapping for Hyper-V

Michael Kelley
2022-11-11T06:22:41Z

With changes to how Hyper-V guest VMs flip memory between private
(encrypted) and shared (decrypted), creating a second kernel virtual
mapping for shared memory is no longer necessary. Everything needed
for the transition to shared is handled by set_memory_decrypted().

As such, remove swiotlb_unencrypted_base and the associated
code.

Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Acked-by: Christoph Hellwig <hch@lst.de>
---
arch/x86/kernel/cpu/mshyperv.c | 7 +------
include/linux/swiotlb.h | 2 --
kernel/dma/swiotlb.c | 45 +-----------------------------------------
3 files changed, 2 insertions(+), 52 deletions(-)

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index b080795..c87e411 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -18,7 +18,6 @@
#include <linux/kexec.h>
#include <linux/i8253.h>
#include <linux/random.h>
-#include <linux/swiotlb.h>
#include <asm/processor.h>
#include <asm/hypervisor.h>
#include <asm/hyperv-tlfs.h>
@@ -332,12 +331,8 @@ static void __init ms_hyperv_init_platform(void)
pr_info("Hyper-V: Isolation Config: Group A 0x%x, Group B 0x%x\n",
ms_hyperv.isolation_config_a, ms_hyperv.isolation_config_b);

- if (hv_get_isolation_type() == HV_ISOLATION_TYPE_SNP) {
+ if (hv_get_isolation_type() == HV_ISOLATION_TYPE_SNP)
static_branch_enable(&isolation_type_snp);
-#ifdef CONFIG_SWIOTLB
- swiotlb_unencrypted_base = ms_hyperv.shared_gpa_boundary;
-#endif
- }
}

if (hv_max_functions_eax >= HYPERV_CPUID_NESTED_FEATURES) {
diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index 35bc4e2..13d7075 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -185,6 +185,4 @@ static inline bool is_swiotlb_for_alloc(struct device *dev)
}
#endif /* CONFIG_DMA_RESTRICTED_POOL */

-extern phys_addr_t swiotlb_unencrypted_base;
-
#endif /* __LINUX_SWIOTLB_H */
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index a34c38b..d3d6be0 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -73,8 +73,6 @@ struct io_tlb_slot {

struct io_tlb_mem io_tlb_default_mem;

-phys_addr_t swiotlb_unencrypted_base;
-
static unsigned long default_nslabs = IO_TLB_DEFAULT_SIZE >> IO_TLB_SHIFT;
static unsigned long default_nareas;

@@ -210,34 +208,6 @@ static inline unsigned long nr_slots(u64 val)
}

/*
- * Remap swioltb memory in the unencrypted physical address space
- * when swiotlb_unencrypted_base is set. (e.g. for Hyper-V AMD SEV-SNP
- * Isolation VMs).
- */
-#ifdef CONFIG_HAS_IOMEM
-static void *swiotlb_mem_remap(struct io_tlb_mem *mem, unsigned long bytes)
-{
- void *vaddr = NULL;
-
- if (swiotlb_unencrypted_base) {
- phys_addr_t paddr = mem->start + swiotlb_unencrypted_base;
-
- vaddr = memremap(paddr, bytes, MEMREMAP_WB);
- if (!vaddr)
- pr_err("Failed to map the unencrypted memory %pa size %lx.\n",
- &paddr, bytes);
- }
-
- return vaddr;
-}
-#else
-static void *swiotlb_mem_remap(struct io_tlb_mem *mem, unsigned long bytes)
-{
- return NULL;
-}
-#endif
-
-/*
* Early SWIOTLB allocation may be too early to allow an architecture to
* perform the desired operations. This function allows the architecture to
* call SWIOTLB when the operations are possible. It needs to be called
@@ -246,18 +216,12 @@ static void *swiotlb_mem_remap(struct io_tlb_mem *mem, unsigned long bytes)
void __init swiotlb_update_mem_attributes(void)
{
struct io_tlb_mem *mem = &io_tlb_default_mem;
- void *vaddr;
unsigned long bytes;

if (!mem->nslabs || mem->late_alloc)
return;
- vaddr = phys_to_virt(mem->start);
bytes = PAGE_ALIGN(mem->nslabs << IO_TLB_SHIFT);
- set_memory_decrypted((unsigned long)vaddr, bytes >> PAGE_SHIFT);
-
- mem->vaddr = swiotlb_mem_remap(mem, bytes);
- if (!mem->vaddr)
- mem->vaddr = vaddr;
+ set_memory_decrypted((unsigned long)mem->vaddr, bytes >> PAGE_SHIFT);
}

static void swiotlb_init_io_tlb_mem(struct io_tlb_mem *mem, phys_addr_t start,
@@ -288,13 +252,6 @@ static void swiotlb_init_io_tlb_mem(struct io_tlb_mem *mem, phys_addr_t start,
mem->slots[i].alloc_size = 0;
}

- /*
- * If swiotlb_unencrypted_base is set, the bounce buffer memory will
- * be remapped and cleared in swiotlb_update_mem_attributes.
- */
- if (swiotlb_unencrypted_base)
- return;
-
memset(vaddr, 0, bytes);
mem->vaddr = vaddr;
return;
--
1.8.3.1