[PATCH] x86/tdx: Optimize try_accept_memory() to reduce 1GB page accepted failed times

[Jun Miao]

Since the current TDX module ABI spec TDG.MEM.PAGE.ACCEPT Leaf show:
"Level of the Secure EPT leaf entry that maps the private page to be
accepted: either 0 (4KB) or 1 (2MB)".

There is not 1G page accept dynamically, if every time try to accept 1G
size but always fail, then cost more time from two cases:
	- When size < 1G, judge failed return 0
	- Really TDCALL<ACCEPT_PAGE> 1G failed when size >= 1G
So skip the 1G and optimize it to 2M directly to save time.

Run the eatmemory with different memories to get the cost time as follow:
	[root@td-guest ~]# ./eatmemory 8G
	Currently total memory: 100169027584
	Currently avail memory: 99901911040
	Eating 8589934592 bytes in chunks of 1024...

	  Start time：1704699207487 ms
	  End time：1704699222966 ms
	  Cost time: 15479 ms
  #
  # Compare with/without this optimization
  #
  # Hardware: ArcherCity Sapphire Rapids 128cores
  # Test eatmemory: https://github.com/jmiao2018/eatmemory.git
  # Detail test log link: https://github.com/jmiao2018/eatmemory/blob/master/log-tdx.txt
  #
  # Accept Memeory Sizes      Before(ms)       After(ms)      Trigger 1G Failed Times      Reduce Time%
  # ....................      ..........       .........      .......................	   .............
  #
		  1G                3414         3402                        751824        -12(-0.035%)
		  2G                3853         3804                       1015126       -349(-0.128%)
		  4G                7773         7561                       1557834       -212(-0.281%)
		  8G               15479        15173                       2633686       -306(-0.201%)
  		 16G               31527        30379                       4785649      -1148(-0.378%)
  		 32G               65058        63723                       9087686      -1335(-0.209%)
		 64G              133379       128354                      17693366      -5025(-0.391%)

Co-developed-by: Zhiquan Li <zhiquan1.li@xxxxxxxxx>
Signed-off-by: Jun Miao <jun.miao@xxxxxxxxx>
---
 arch/x86/coco/tdx/tdx-shared.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/arch/x86/coco/tdx/tdx-shared.c b/arch/x86/coco/tdx/tdx-shared.c
index 1655aa56a0a5..1694b7eba93b 100644
--- a/arch/x86/coco/tdx/tdx-shared.c
+++ b/arch/x86/coco/tdx/tdx-shared.c
@@ -18,7 +18,7 @@ static unsigned long try_accept_one(phys_addr_t start, unsigned long len,
 	 * Pass the page physical address to the TDX module to accept the
 	 * pending, private page.
 	 *
-	 * Bits 2:0 of RCX encode page size: 0 - 4K, 1 - 2M, 2 - 1G.
+	 * Bits 2:0 of RCX encode page size: 0 - 4K, 1 - 2M.
 	 */
 	switch (pg_level) {
 	case PG_LEVEL_4K:
@@ -27,9 +27,6 @@ static unsigned long try_accept_one(phys_addr_t start, unsigned long len,
 	case PG_LEVEL_2M:
 		page_size = TDX_PS_2M;
 		break;
-	case PG_LEVEL_1G:
-		page_size = TDX_PS_1G;
-		break;
 	default:
 		return 0;
 	}
@@ -55,11 +52,14 @@ bool tdx_accept_memory(phys_addr_t start, phys_addr_t end)
 		 * Try larger accepts first. It gives chance to VMM to keep
 		 * 1G/2M Secure EPT entries where possible and speeds up
 		 * process by cutting number of hypercalls (if successful).
-		 */
+		 * Since per current TDX spec, only support for adding 4KB or
+		 * 2MB page dynamically.
+		 * /
 
-		accept_size = try_accept_one(start, len, PG_LEVEL_1G);
-		if (!accept_size)
+		if (IS_ALIGNED(start, PMD_SIZE) && len >= PMD_SIZE)
 			accept_size = try_accept_one(start, len, PG_LEVEL_2M);
+
+		/* The 4KB page case or accept 2MB page failed case. */
 		if (!accept_size)
 			accept_size = try_accept_one(start, len, PG_LEVEL_4K);
 		if (!accept_size)
-- 
2.32.0