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Message-ID: <20201104221452.GA26079@char.us.oracle.com>
Date: Wed, 4 Nov 2020 17:14:52 -0500
From: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To: Ashish Kalra <Ashish.Kalra@....com>
Cc: hch@....de, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
hpa@...or.com, x86@...nel.org, luto@...nel.org,
peterz@...radead.org, dave.hansen@...ux-intel.com,
iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
brijesh.singh@....com, Thomas.Lendacky@....com,
ssg.sos.patches@....com
Subject: Re: [PATCH v3] swiotlb: Adjust SWIOTBL bounce buffer size for SEV
guests.
On Wed, Nov 04, 2020 at 10:08:04PM +0000, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@....com>
>
> For SEV, all DMA to and from guest has to use shared
> (un-encrypted) pages. SEV uses SWIOTLB to make this
> happen without requiring changes to device drivers.
> However, depending on workload being run, the default
> 64MB of SWIOTLB might not be enough and SWIOTLB
> may run out of buffers to use for DMA, resulting
> in I/O errors and/or performance degradation for
> high I/O workloads.
>
> Increase the default size of SWIOTLB for SEV guests
> using a minimum value of 128MB and a maximum value
<blinks>
64MB for a 1GB VM is not enough?
> of 512MB, determining on amount of provisioned guest
I like the implementation on how this is done.. but
the choices of memory and how much seems very much
random. Could there be some math behind this?
> memory.
>
> Using late_initcall() interface to invoke
> swiotlb_adjust() does not work as the size
> adjustment needs to be done before mem_encrypt_init()
> and reserve_crashkernel() which use the allocated
> SWIOTLB buffer size, hence calling it explicitly
> from setup_arch().
>
> The SWIOTLB default size adjustment is added as an
> architecture specific interface/callback to allow
> architectures such as those supporting memory
> encryption to adjust/expand SWIOTLB size for their
> use.
>
> Signed-off-by: Ashish Kalra <ashish.kalra@....com>
> ---
> arch/x86/kernel/setup.c | 2 ++
> arch/x86/mm/mem_encrypt.c | 42 +++++++++++++++++++++++++++++++++++++++
> include/linux/swiotlb.h | 1 +
> kernel/dma/swiotlb.c | 27 +++++++++++++++++++++++++
> 4 files changed, 72 insertions(+)
>
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 3511736fbc74..b073d58dd4a3 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -1166,6 +1166,8 @@ void __init setup_arch(char **cmdline_p)
> if (boot_cpu_has(X86_FEATURE_GBPAGES))
> hugetlb_cma_reserve(PUD_SHIFT - PAGE_SHIFT);
>
> + swiotlb_adjust();
> +
> /*
> * Reserve memory for crash kernel after SRAT is parsed so that it
> * won't consume hotpluggable memory.
> diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
> index 3f248f0d0e07..e0deb157cddd 100644
> --- a/arch/x86/mm/mem_encrypt.c
> +++ b/arch/x86/mm/mem_encrypt.c
> @@ -489,7 +489,49 @@ static void print_mem_encrypt_feature_info(void)
> pr_cont("\n");
> }
>
> +#define TOTAL_MEM_1G 0x40000000UL
> +#define TOTAL_MEM_4G 0x100000000UL
> +
> +#define SIZE_128M (128UL<<20)
> +#define SIZE_256M (256UL<<20)
> +#define SIZE_512M (512UL<<20)
> +
> /* Architecture __weak replacement functions */
> +unsigned long __init arch_swiotlb_adjust(unsigned long iotlb_default_size)
> +{
> + unsigned long size = 0;
> +
> + /*
> + * For SEV, all DMA has to occur via shared/unencrypted pages.
> + * SEV uses SWOTLB to make this happen without changing device
> + * drivers. However, depending on the workload being run, the
> + * default 64MB of SWIOTLB may not be enough & SWIOTLB may
> + * run out of buffers for DMA, resulting in I/O errors and/or
> + * performance degradation especially with high I/O workloads.
> + * Increase the default size of SWIOTLB for SEV guests using
> + * a minimum value of 128MB and a maximum value of 512MB,
> + * depending on amount of provisioned guest memory.
> + */
> + if (sev_active()) {
> + phys_addr_t total_mem = memblock_phys_mem_size();
> +
> + if (total_mem <= TOTAL_MEM_1G)
> + size = clamp(iotlb_default_size * 2, SIZE_128M,
> + SIZE_128M);
> + else if (total_mem <= TOTAL_MEM_4G)
> + size = clamp(iotlb_default_size * 4, SIZE_256M,
> + SIZE_256M);
> + else
> + size = clamp(iotlb_default_size * 8, SIZE_512M,
> + SIZE_512M);
> +
> + pr_info("SEV adjusted max SWIOTLB size = %luMB",
> + size >> 20);
> + }
> +
> + return size;
> +}
> +
> void __init mem_encrypt_init(void)
> {
> if (!sme_me_mask)
> diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
> index 046bb94bd4d6..01ae6d891327 100644
> --- a/include/linux/swiotlb.h
> +++ b/include/linux/swiotlb.h
> @@ -33,6 +33,7 @@ extern void swiotlb_init(int verbose);
> int swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose);
> extern unsigned long swiotlb_nr_tbl(void);
> unsigned long swiotlb_size_or_default(void);
> +extern void __init swiotlb_adjust(void);
> extern int swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs);
> extern void __init swiotlb_update_mem_attributes(void);
>
> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index c19379fabd20..66a9e627bb51 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -163,6 +163,33 @@ unsigned long swiotlb_size_or_default(void)
> return size ? size : (IO_TLB_DEFAULT_SIZE);
> }
>
> +unsigned long __init __weak arch_swiotlb_adjust(unsigned long size)
> +{
> + return 0;
> +}
> +
> +void __init swiotlb_adjust(void)
> +{
> + unsigned long size;
> +
> + /*
> + * If swiotlb parameter has not been specified, give a chance to
> + * architectures such as those supporting memory encryption to
> + * adjust/expand SWIOTLB size for their use.
> + */
> + if (!io_tlb_nslabs) {
> + size = arch_swiotlb_adjust(IO_TLB_DEFAULT_SIZE);
> + if (size) {
> + size = ALIGN(size, 1 << IO_TLB_SHIFT);
> + io_tlb_nslabs = size >> IO_TLB_SHIFT;
> + io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE);
> +
> + pr_info("architecture adjusted SWIOTLB slabs = %lu\n",
> + io_tlb_nslabs);
> + }
> + }
> +}
> +
> void swiotlb_print_info(void)
> {
> unsigned long bytes = io_tlb_nslabs << IO_TLB_SHIFT;
> --
> 2.17.1
>
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