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Re: [Qemu-ppc] [PATCH] spapr_iommu: fix erroneous sanity check in h_put_

From: Alexey Kardashevskiy
Subject: Re: [Qemu-ppc] [PATCH] spapr_iommu: fix erroneous sanity check in h_put_tce_indirect()
Date: Wed, 17 Jun 2015 00:32:46 +1000
User-agent: Mozilla/5.0 (X11; Linux i686 on x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0

On 06/16/2015 07:24 PM, Greg Kurz wrote:
On Tue, 16 Jun 2015 18:53:51 +1000
Alexey Kardashevskiy <address@hidden> wrote:

On 06/16/2015 03:28 AM, Greg Kurz wrote:
According to PAPR+, the TCE is implemented as follows:
        bits  0-51: real page number
        bits 52-61: reserved for future use
        bits 62-63: page protection (read-only, write-only, read-write)

tce_list is not a TCE, it is "The logical address of a page of (4 K long on
a 4 K boundary) of TCE contents to be stored in the TCE table (contains
logical address of storage page to be mapped)" so we rather want to remove
(tce_list & ~SPAPR_TCE_RW) below.

Oops my bad for the confustion... :-\

Then it looks like SPAPR_TCE_RW can be dropped as well since put_tce_emu() uses
IOMMU_RW instead.

Well, spapr_tce_translate_iommu() should actually translate SPAPR_TCE_xxx (PAPR defined flags) to IOMMU_xxx (QEMU IOMMUTLBEntry permission bits), not just rely on the fact that they match.

Possible values for the protection bits are necessarly non-zero and thus
H_PUT_TCE_INDIRECT currently always fails and returns H_PARAMETER.

The code explicitly clears the protection bits when computing the TCE offset,
a few lines below (tce_list & ~SPAPR_TCE_RW)... The sanity check is obviously
wrong for these bits.

Moreover, I could find no indication in PAPR+ that using the other reserved
bits should error out with H_PARAMETER.

This patch simply drops the offending check.

Signed-off-by: Greg Kurz <address@hidden>
   hw/ppc/spapr_iommu.c |    2 +-
   1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/ppc/spapr_iommu.c b/hw/ppc/spapr_iommu.c
index 8cd9dba9ac4d..37a1110c9d87 100644
--- a/hw/ppc/spapr_iommu.c
+++ b/hw/ppc/spapr_iommu.c
@@ -258,7 +258,7 @@ static target_ulong h_put_tce_indirect(PowerPCCPU *cpu,
           return H_PARAMETER;

-    if ((npages > 512) || (tce_list & SPAPR_TCE_PAGE_MASK)) {
+    if (npages > 512) {
           return H_PARAMETER;


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