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Message-ID: <20201208222220.GA27599@char.us.oracle.com>
Date: Tue, 8 Dec 2020 17:22:20 -0500
From: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To: Ashish Kalra <Ashish.Kalra@....com>
Cc: hch@....de, tglx@...utronix.de, mingo@...hat.com, 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, Jon.Grimm@....com, rientjes@...gle.com
Subject: Re: [PATCH v8] swiotlb: Adjust SWIOTBL bounce buffer size for SEV
guests.
On Mon, Dec 07, 2020 at 11:10:57PM +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.
>
> Adjust the default size of SWIOTLB for SEV guests using a
> percentage of the total memory available to guest for SWIOTLB buffers.
>
> 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 call it explicitly from setup_arch().
>
> The SWIOTLB default size adjustment needs to be added as an architecture
> specific interface/callback to allow architectures such as those supporting
> memory encryption to adjust/expand SWIOTLB size for their use.
>
> v5 fixed build errors and warnings as
> Reported-by: kbuild test robot <lkp@...el.com>
>
> Signed-off-by: Ashish Kalra <ashish.kalra@....com>
> ---
> arch/x86/kernel/setup.c | 2 ++
> arch/x86/mm/mem_encrypt.c | 37 +++++++++++++++++++++++++++++++++++++
> include/linux/swiotlb.h | 6 ++++++
> kernel/dma/swiotlb.c | 22 ++++++++++++++++++++++
> 4 files changed, 67 insertions(+)
>
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 84f581c91db4..31e24e198061 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -1149,6 +1149,8 @@ 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 1bcfbcd2bfd7..d1b8d60040cf 100644
> --- a/arch/x86/mm/mem_encrypt.c
> +++ b/arch/x86/mm/mem_encrypt.c
> @@ -485,7 +485,44 @@ static void print_mem_encrypt_feature_info(void)
> pr_cont("\n");
> }
>
> +/*
> + * The percentage of guest memory used here for SWIOTLB buffers
> + * is more of an approximation of the static adjustment which
> + * is 128M for <1G guests, 256M for 1G-4G guests and 512M for >4G guests.
No?
it is 64MB for <1G, and ~128M to 256M for 1G-to-4G
I will fix it up.
> + */
> +#define SEV_ADJUST_SWIOTLB_SIZE_PERCENT 6
> +
> /* Architecture __weak replacement functions */
> +unsigned long __init arch_swiotlb_adjust(unsigned long iotlb_default_size)
> +{
> + unsigned long size = iotlb_default_size;
> +
> + /*
> + * 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 and`SWIOTLB may
> + * run out of buffers for DMA, resulting in I/O errors and/or
> + * performance degradation especially with high I/O workloads.
> + * Adjust the default size of SWIOTLB for SEV guests using
> + * a percentage of guest memory for SWIOTLB buffers.
> + * Also as the SWIOTLB bounce buffer memory is allocated
> + * from low memory, ensure that the adjusted size is within
> + * the limits of low available memory.
> + *
> + */
> + if (sev_active()) {
> + phys_addr_t total_mem = memblock_phys_mem_size();
> +
> + size = total_mem * SEV_ADJUST_SWIOTLB_SIZE_PERCENT / 100;
> + size = clamp_val(size, iotlb_default_size, SZ_1G);
> + pr_info("SWIOTLB bounce buffer size adjusted to %luMB for SEV",
> + 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 3bb72266a75a..b5904fa4b67c 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);
> +unsigned long __init arch_swiotlb_adjust(unsigned long size);
> 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);
> @@ -77,6 +78,7 @@ void __init swiotlb_exit(void);
> unsigned int swiotlb_max_segment(void);
> size_t swiotlb_max_mapping_size(struct device *dev);
> bool is_swiotlb_active(void);
> +void __init swiotlb_adjust(void);
> #else
> #define swiotlb_force SWIOTLB_NO_FORCE
> static inline bool is_swiotlb_buffer(phys_addr_t paddr)
> @@ -99,6 +101,10 @@ static inline bool is_swiotlb_active(void)
> {
> return false;
> }
> +
> +static inline void swiotlb_adjust(void)
> +{
> +}
> #endif /* CONFIG_SWIOTLB */
>
> extern void swiotlb_print_info(void);
> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index 781b9dca197c..0150ca2336bc 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -163,6 +163,28 @@ 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 size;
> +}
> +
> +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);
> + size = ALIGN(size, 1 << IO_TLB_SHIFT);
> + io_tlb_nslabs = size >> IO_TLB_SHIFT;
> + io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE);
> + }
> +}
> +
> void swiotlb_print_info(void)
> {
> unsigned long bytes = io_tlb_nslabs << IO_TLB_SHIFT;
> --
> 2.17.1
>
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