x86/hyperv/Swiotlb: Add swiotlb_alloc_from_low_pages switch
cover x86/hyperv/Swiotlb: Add swiotlb_alloc_from_low_pages switch
From: Tianyu Lan <[email protected]>
Hyper-V Isolation VM may fail to allocate swiotlb bounce buffer due to there is no enough contiguous memory from 0 to 4G in some cases. Current swiotlb code allocate bounce buffer in the low end memory. This patchset adds a switch "swiotlb_alloc_from_low_pages" and it's set to true by default. Platform may clear it if necessary. Devices in Hyper-V Isolation VM may use memory above 4G as DMA memory and set the switch to false in order to avoid no enough contiguous memory in low end address space.
Tianyu Lan (2):
Swiotlb: Add swiotlb_alloc_from_low_pages switch x86/hyperv: Set swiotlb_alloc_from_low_pages to false
arch/x86/kernel/cpu/mshyperv.c | 1 + include/linux/swiotlb.h | 1 + kernel/dma/swiotlb.c | 13 +++++++++++-- 3 files changed, 13 insertions(+), 2 deletions(-)
Signature · 1 line
2.25.1
PATCH 1/2 Swiotlb: Add swiotlb_alloc_from_low_pages switch
From: Tianyu Lan <[email protected]>
Hyper-V Isolation VM and AMD SEV VM uses swiotlb bounce buffer to share memory with hypervisor. Current swiotlb bounce buffer is only allocated from 0 to ARCH_LOW_ADDRESS_LIMIT which is default to 0xffffffffUL. Isolation VM and AMD SEV VM needs 1G bounce buffer at most. This will fail when there is not enough contiguous memory from 0 to 4G address space and devices also may use memory above 4G address space as DMA memory. Expose swiotlb_alloc_from_low_pages and platform mey set it to false when it's not necessary to limit bounce buffer from 0 to 4G memory.
--- include/linux/swiotlb.h | 1 + kernel/dma/swiotlb.c | 13 +++++++++++-- 2 files changed, 12 insertions(+), 2 deletions(-)
include/linux/swiotlb.h +1 -0
@@ -191,5 +191,6 @@ static inline bool is_swiotlb_for_alloc(struct device *dev)#endif /* CONFIG_DMA_RESTRICTED_POOL */ extern phys_addr_t swiotlb_unencrypted_base; +extern bool swiotlb_alloc_from_low_pages;#endif /* __LINUX_SWIOTLB_H */
kernel/dma/swiotlb.c +11 -2
@@ -73,6 +73,12 @@ enum swiotlb_force swiotlb_force;struct io_tlb_mem io_tlb_default_mem; +/* +* Get IO TLB memory from the low pages if swiotlb_alloc_from_low_pages +* is set. +*/ +bool swiotlb_alloc_from_low_pages = true; +phys_addr_t swiotlb_unencrypted_base;/*
@@ -284,8 +290,11 @@ swiotlb_init(int verbose)if (swiotlb_force ==SWIOTLB_NO_FORCE )return ; -/* Get IO TLB memory from the low pages */ - tlb =memblock_alloc_low (bytes,PAGE_SIZE ); +if (swiotlb_alloc_from_low_pages) + tlb =memblock_alloc_low (bytes,PAGE_SIZE ); +else + tlb =memblock_alloc (bytes,PAGE_SIZE ); +if (!tlb) goto fail;if (swiotlb_init_with_tbl (tlb, default_nslabs, verbose))
Signature · 1 line
2.25.1
RE: [PATCH 1/2] Swiotlb: Add swiotlb_alloc_from_low_pages switch
From: Tianyu Lan <[email protected]> Sent: Wednesday, January 26, 2022 8:11 AM
Quoted 59 lines
Hyper-V Isolation VM and AMD SEV VM uses swiotlb bounce buffer to share memory with hypervisor. Current swiotlb bounce buffer is only allocated from 0 to
ARCH_LOW_ADDRESS_LIMITwhich is default to0xffffffffUL. Isolation VM and AMD SEV VM needs 1G bounce buffer at most. This will fail when there is not enough contiguous memory from 0 to 4G address space and devices also may use memory above 4G address space as DMA memory. Exposeswiotlb_alloc_from_low_pagesand platform mey set it to false when it's not necessary to limit bounce buffer from 0 to 4G memory.Signed-off-by Tianyu Lan <[email protected]>--- include/linux/swiotlb.h | 1 + kernel/dma/swiotlb.c | 13 +++++++++++-- 2 files changed, 12 insertions(+), 2 deletions(-)include/linux/swiotlb.h +1
-0@@ -191,5 +191,6 @@ static inline bool is_swiotlb_for_alloc(struct device *dev)#endif /* CONFIG_DMA_RESTRICTED_POOL */ extern phys_addr_t swiotlb_unencrypted_base; +extern bool swiotlb_alloc_from_low_pages;#endif /* __LINUX_SWIOTLB_H */ kernel/dma/swiotlb.c +11
-3@@ -73,6 +73,12 @@ enum swiotlb_force swiotlb_force;struct io_tlb_mem io_tlb_default_mem; +/* +* Get IO TLB memory from the low pages if swiotlb_alloc_from_low_pages +* is set. +*/ +bool swiotlb_alloc_from_low_pages = true; +phys_addr_t swiotlb_unencrypted_base;/* @@ -284,8 +290,11 @@ swiotlb_init(int verbose)if (swiotlb_force ==SWIOTLB_NO_FORCE )return ; -/* Get IO TLB memory from the low pages */ - tlb =memblock_alloc_low (bytes,PAGE_SIZE ); +if (swiotlb_alloc_from_low_pages) + tlb =memblock_alloc_low (bytes,PAGE_SIZE ); +else + tlb =memblock_alloc (bytes,PAGE_SIZE ); +if (!tlb) goto fail;if (swiotlb_init_with_tbl (tlb, default_nslabs, verbose)) --
Quoted 1 line
2.25.1
PATCH 2/2 x86/hyperv: Set swiotlb_alloc_from_low_pages to false
In reply to Tianyu LanFrom: Tianyu Lan <[email protected]>
In Hyper-V Isolation VM, swiotlb bnounce buffer size maybe 1G at most and there maybe no enough memory from 0 to 4G according to memory layout. Devices in Isolation VM can use memory above 4G as DMA memory. Set swiotlb_ alloc_from_low_pages to false in Isolation VM.
--- arch/x86/kernel/cpu/mshyperv.c | 1 + 1 file changed, 1 insertion(+)
arch/x86/kernel/cpu/mshyperv.c +1 -0
@@ -343,6 +343,7 @@ static void __init ms_hyperv_init_platform(void)* use swiotlb bounce buffer for dma transaction. */ swiotlb_force =SWIOTLB_FORCE ; + swiotlb_alloc_from_low_pages = false;#endif }
Signature · 1 line
2.25.1
RE: [PATCH 2/2] x86/hyperv: Set swiotlb_alloc_from_low_pages to false
From: Tianyu Lan <[email protected]> Sent: Wednesday, January 26, 2022 8:11 AM
Quoted 24 lines
In Hyper-V Isolation VM, swiotlb bnounce buffer size maybe 1G at most and there maybe no enough memory from 0 to 4G according to memory layout. Devices in Isolation VM can use memory above 4G as DMA memory. Set
swiotlb_alloc_from_low_pagesto false in Isolation VM.Signed-off-by Tianyu Lan <[email protected]>--- arch/x86/kernel/cpu/mshyperv.c | 1 + 1 file changed, 1 insertion(+)arch/x86/kernel/cpu/mshyperv.c +1
-1@@ -343,6 +343,7 @@ static void __init ms_hyperv_init_platform(void)* use swiotlb bounce buffer for dma transaction. */ swiotlb_force =SWIOTLB_FORCE ; + swiotlb_alloc_from_low_pages = false;#endif } --
Quoted 1 line
2.25.1
I think this interface is a little too hacky. In the end all the non-trusted hypervisor schemes (including the per-device swiotlb one) can allocate the memory from everywhere and want for force use of swiotlb. I think we need some kind of proper interface for that instead of setting all kinds of global variables.
Robin Murphy
reviewerQuoted 5 lines · Christoph Hellwig
I think this interface is a little too hacky. In the end all the non-trusted hypervisor schemes (including the per-device swiotlb one) can allocate the memory from everywhere and want for force use of swiotlb. I think we need some kind of proper interface for that instead of setting all kinds of global variables.
Right, if platform/hypervisor code knows enough to be able to set magic non-standard allocation flags correctly, surely it could equally just perform whatever non-standard allocation it needs and call swiotlb_init_with_tbl() instead of swiotlb_init().
Robin.
Quoted 5 lines · Christoph Hellwig
I think this interface is a little too hacky. In the end all the non-trusted hypervisor schemes (including the per-device swiotlb one) can allocate the memory from everywhere and want for force use of swiotlb. I think we need some kind of proper interface for that instead of setting all kinds of global variables.
Hi Christoph:
Thanks for your review. I draft the following patch to export a
interface swiotlb_set_alloc_from_low_pages(). Could you have a look whether this looks good for you.
include/linux/swiotlb.h +1 -0
@@ -39,6 +39,7 @@ enum swiotlb_force {extern void swiotlb_init (int verbose);int swiotlb_init_with_tbl (char *tlb,unsigned long nslabs,int verbose);unsigned long swiotlb_size_or_default (void ); +void swiotlb_set_alloc_from_low_pages (bool low);extern int swiotlb_late_init_with_tbl (char *tlb,unsigned long nslabs);extern int swiotlb_late_init_with_default_size (size_t default_size);extern void __init swiotlb_update_mem_attributes (void );
kernel/dma/swiotlb.c +16 -2
@@ -73,6 +73,8 @@ enum swiotlb_force swiotlb_force;struct io_tlb_mem io_tlb_default_mem; +static bool swiotlb_alloc_from_low_pages = true; +phys_addr_t swiotlb_unencrypted_base;/*
@@ -116,6 +118,11 @@ void swiotlb_set_max_segment(unsigned int val) max_segment =rounddown (val,PAGE_SIZE ); } +void swiotlb_set_alloc_from_low_pages (bool low) +{ + swiotlb_alloc_from_low_pages = low; +} +unsigned long swiotlb_size_or_default (void ) {return default_nslabs <<IO_TLB_SHIFT ;
@@ -284,8 +291,15 @@ swiotlb_init(int verbose)if (swiotlb_force ==SWIOTLB_NO_FORCE )return ; -/* Get IO TLB memory from the low pages */ - tlb =memblock_alloc_low (bytes,PAGE_SIZE ); +/* +* Get IO TLB memory from the low pages if swiotlb_alloc_from_low_pages +* is set. +*/ +if (swiotlb_alloc_from_low_pages) + tlb =memblock_alloc_low (bytes,PAGE_SIZE ); +else + tlb =memblock_alloc (bytes,PAGE_SIZE ); +if (!tlb) goto fail;if (swiotlb_init_with_tbl (tlb, default_nslabs, verbose))