Merge branch 'stable/for-linus-5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/swiotlb

Pull swiotlb update from Konrad Rzeszutek Wilk:
 "A generic (but for right now engaged only with AMD SEV) mechanism to
  adjust a larger size SWIOTLB based on the total memory of the SEV
  guests which right now require the bounce buffer for interacting with
  the outside world.

  Normal knobs (swiotlb=XYZ) still work"

* 'stable/for-linus-5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/swiotlb:
  x86,swiotlb: Adjust SWIOTLB bounce buffer size for SEV guests

3 files changed, 39 insertions, 0 deletions

diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
index 2f62bbdd9d12..31c4df123aa0 100644
--- a/arch/x86/include/asm/mem_encrypt.h
+++ b/arch/x86/include/asm/mem_encrypt.h
@@ -37,6 +37,7 @@ void __init sme_map_bootdata(char *real_mode_data);
 void __init sme_unmap_bootdata(char *real_mode_data);
 
 void __init sme_early_init(void);
+void __init sev_setup_arch(void);
 
 void __init sme_encrypt_kernel(struct boot_params *bp);
 void __init sme_enable(struct boot_params *bp);
@@ -69,6 +70,7 @@ static inline void __init sme_map_bootdata(char *real_mode_data) { }
 static inline void __init sme_unmap_bootdata(char *real_mode_data) { }
 
 static inline void __init sme_early_init(void) { }
+static inline void __init sev_setup_arch(void) { }
 
 static inline void __init sme_encrypt_kernel(struct boot_params *bp) { }
 static inline void __init sme_enable(struct boot_params *bp) { }
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index a23130c86bdd..740f3bdb3f61 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -1049,6 +1049,12 @@ void __init setup_arch(char **cmdline_p)
 	memblock_set_current_limit(ISA_END_ADDRESS);
 	e820__memblock_setup();
 
+	/*
+	 * Needs to run after memblock setup because it needs the physical
+	 * memory size.
+	 */
+	sev_setup_arch();
+
 	reserve_bios_regions();
 
 	efi_fake_memmap();
diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index bc0833713be9..c79e5736ab2b 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -198,6 +198,37 @@ void __init sme_early_init(void)
 		swiotlb_force = SWIOTLB_FORCE;
 }
 
+void __init sev_setup_arch(void)
+{
+	phys_addr_t total_mem = memblock_phys_mem_size();
+	unsigned long size;
+
+	if (!sev_active())
+		return;
+
+	/*
+	 * For SEV, all DMA has to occur via shared/unencrypted pages.
+	 * SEV uses SWIOTLB 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.
+	 *
+	 * The percentage of guest memory used here for SWIOTLB buffers
+	 * is more of an approximation of the static adjustment which
+	 * 64MB for <1G, and ~128M to 256M for 1G-to-4G, i.e., the 6%
+	 */
+	size = total_mem * 6 / 100;
+	size = clamp_val(size, IO_TLB_DEFAULT_SIZE, SZ_1G);
+	swiotlb_adjust_size(size);
+}
+
 static void __init __set_clr_pte_enc(pte_t *kpte, int level, bool enc)
 {
 	pgprot_t old_prot, new_prot;