linux-kernel - [PATCH v2] cxl/mem: Fix register block offset calculation

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Date:   Thu, 15 Apr 2021 19:49:12 -0700
From:   Ben Widawsky <ben.widawsky@...el.com>
To:     linux-cxl@...r.kernel.org
Cc:     Ben Widawsky <ben.widawsky@...el.com>, linux-pci@...r.kernel.org,
        linux-acpi@...r.kernel.org, ira.weiny@...el.com,
        vishal.l.verma@...el.com, alison.schofield@...el.com,
        dan.j.williams@...el.com, linux-kernel@...r.kernel.org
Subject: [PATCH v2] cxl/mem: Fix register block offset calculation

The offset for the register block should be a 64K aligned value, and
therefore FIELD_GET (which will shift) is not correct for the
calculation.

>From 8.1.9.1 of the CXL 2.0 spec:
  A[31:16] of offset from the address contained by one of the Function's
  Base Address Registers to point to the base of the Register Block.
  Register Block Offset is 64K aligned. Hence A[15:0] is zero

The "Register Offset Low" register of a "DVSEC Register Locator"
contains the 64K aligned offset for the registers along with the BAR
indicator and an ID. The implementation was treating the "Register Block
Offset Low" field a value rather than as a pre-aligned component of the
64-bit offset. So, just mask, don't mask and shift (FIELD_GET).

This wasn't found earlier because the primary development done in the
QEMU environment only uses 0 offsets

Fixes: 8adaf747c9f0 ("cxl/mem: Find device capabilities")
Reported-by: Vishal Verma <vishal.l.verma@...el.com>
Signed-off-by: Ben Widawsky <ben.widawsky@...el.com>
---
 drivers/cxl/mem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
index e3003f49b329..1b5078311f7d 100644
--- a/drivers/cxl/mem.c
+++ b/drivers/cxl/mem.c
@@ -998,7 +998,7 @@ static struct cxl_mem *cxl_mem_create(struct pci_dev *pdev, u32 reg_lo,
 		return NULL;
 	}
 
-	offset = ((u64)reg_hi << 32) | FIELD_GET(CXL_REGLOC_ADDR_MASK, reg_lo);
+	offset = ((u64)reg_hi << 32) | (reg_lo & CXL_REGLOC_ADDR_MASK);
 	bar = FIELD_GET(CXL_REGLOC_BIR_MASK, reg_lo);
 
 	/* Basic sanity check that BAR is big enough */
-- 
2.31.1