EDAC/ghes: Fix grain calculation

The current code to convert a physical address mask to a grain
(defined as granularity in bytes) is:

	e->grain = ~(mem_err->physical_addr_mask & ~PAGE_MASK);

This is broken in several ways:

1) It calculates to wrong grain values. E.g., a physical address mask
of ~0xfff should give a grain of 0x1000. Without considering
PAGE_MASK, there is an off-by-one. Things are worse when also
filtering it with ~PAGE_MASK. This will calculate to a grain with the
upper bits set. In the example it even calculates to ~0.

2) The grain does not depend on and is unrelated to the kernel's
page-size. The page-size only matters when unmapping memory in
memory_failure(). Smaller grains are wrongly rounded up to the
page-size, on architectures with a configurable page-size (e.g. arm64)
this could round up to the even bigger page-size of the hypervisor.

Fix this with:

	e->grain = ~mem_err->physical_addr_mask + 1;

The grain_bits are defined as:

	grain = 1 << grain_bits;

Change also the grain_bits calculation accordingly, it is the same
formula as in edac_mc.c now and the code can be unified.

The value in ->physical_addr_mask coming from firmware is assumed to
be contiguous, but this is not sanity-checked. However, in case the
mask is non-contiguous, a conversion to grain_bits effectively
converts the grain bit mask to a power of 2 by rounding it up.

Suggested-by: James Morse <james.morse@arm.com>
Signed-off-by: Robert Richter <rrichter@marvell.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Cc: "linux-edac@vger.kernel.org" <linux-edac@vger.kernel.org>
Cc: Tony Luck <tony.luck@intel.com>
Link: https://lkml.kernel.org/r/20191106093239.25517-11-rrichter@marvell.com

diff --git a/drivers/edac/ghes_edac.c b/drivers/edac/ghes_edac.c
index 5dc53d3..e24fbba 100644 (file)
--- a/drivers/edac/ghes_edac.c
+++ b/drivers/edac/ghes_edac.c
@@ -230,6 +230,7 @@ void ghes_edac_report_mem_error(int sev, struct cper_sec_mem_err *mem_err)
        /* Cleans the error report buffer */
        memset(e, 0, sizeof (*e));
        e->error_count = 1;
+       e->grain = 1;
        strcpy(e->label, "unknown label");
        e->msg = pvt->msg;
        e->other_detail = pvt->other_detail;
@@ -325,7 +326,7 @@ void ghes_edac_report_mem_error(int sev, struct cper_sec_mem_err *mem_err)
 
        /* Error grain */
        if (mem_err->validation_bits & CPER_MEM_VALID_PA_MASK)
-               e->grain = ~(mem_err->physical_addr_mask & ~PAGE_MASK);
+               e->grain = ~mem_err->physical_addr_mask + 1;
 
        /* Memory error location, mapped on e->location */
        p = e->location;
@@ -441,8 +442,13 @@ void ghes_edac_report_mem_error(int sev, struct cper_sec_mem_err *mem_err)
        if (p > pvt->other_detail)
                *(p - 1) = '\0';
 
+       /* Sanity-check driver-supplied grain value. */
+       if (WARN_ON_ONCE(!e->grain))
+               e->grain = 1;
+
+       grain_bits = fls_long(e->grain - 1);
+
        /* Generate the trace event */
-       grain_bits = fls_long(e->grain);
        snprintf(pvt->detail_location, sizeof(pvt->detail_location),
                 "APEI location: %s %s", e->location, e->other_detail);
        trace_mc_event(type, e->msg, e->label, e->error_count,