Re: [PATCH] hw/arm/virt: use pflash image real size when mapping

["haibinzhang(张海斌)" <haibinzhang@tencent.com>]

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On Sep 18, 2020, at 9:41 PM, Philippe Mathieu-Daudé <philmd@redhat.com<mailto:philmd@redhat.com>> wrote:

Cc'ing firmware experts.

On 9/18/20 2:26 PM, haibinzhang(寮犳捣鏂? wrote:
Default size of arm-virt pflash image is 64MB which
will cost extra 128MB(64MBx2) memory per qemu process
and 12.5GB for 100 qemu processes. Host memory is
precious and it is valuable to reduce pflash image size.
For compatibility arm-virt uses real size when mapping.

Flash#0 is a device because eventually its model will handle
sector/block protection, so firmware can do CapsuleUpdate
(updating itself). Meanwhile you could treat flash#0 as a pure
ROM device... But this wouldn't be the 'arm-virt' machine anymore.


Example:
1. Get QEMU_EFI.fd and QEMU_VARS.fd from tianocore/edk2

2. Make pflash images
  dd if=/dev/zero bs=1M count=64 of=flash0.img
  dd if=/dev/zero bs=1M count=64 of=flash1.img
  dd if=QEMU_EFI.fd bs=1M of=flash0.img conv=notrunc
  dd if=QEMU_VARS.fd bs=1M of=flash1.img conv=notrunc

3. Start VM
  qemu-system-aarch64 -machine virt,accel=kvm,gic-version=3 \
  -drive file=flash0.img,if=pflash,format=raw,unit=0,readonly=on \
  -drive file=flash1.img,if=pflash,format=raw,unit=1 \
  …

In virt machine, VIRT_FLASH size is fixed 128MB (fixed 64MB for Flash0, fixed 64MB for Flash1).
Flash0 and Flash1 are two Block Backend devices and will be copied into two memory storages alloced
in virt_flash_map, not file mapping. Size of memory storage is fixed 64MB.

Since size checking, virt machine currently doesn’t support <64MB pflash images. So, get real
size of pflash image first, and use real size to alloc memory storage.

I always use 8MB Flash0 and Flash1, using following commands
  dd if=/dev/zero bs=1M count=8 of=flash0.img
  dd if=/dev/zero bs=1M count=8 of=flash1.img
  dd if=QEMU_EFI.fd bs=1M of=flash0.img conv=notrunc
  dd if=QEMU_VARS.fd bs=1M of=flash1.img conv=notrunc


Signed-off-by: Haibin Zhang <haibinzhang@tencent.com<mailto:haibinzhang@tencent.com>>
---
hw/arm/virt.c | 22 ++++++++++++++++++++--
1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index acf9bfbece..3545e12865 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -50,6 +50,7 @@
#include "sysemu/sysemu.h"
#include "sysemu/tpm.h"
#include "sysemu/kvm.h"
+#include "sysemu/block-backend.h"
#include "hw/loader.h"
#include "exec/address-spaces.h"
#include "qemu/bitops.h"
@@ -1001,10 +1002,27 @@ static void virt_flash_map(VirtMachineState *vms,
     */
    hwaddr flashsize = vms->memmap[VIRT_FLASH].size / 2;
    hwaddr flashbase = vms->memmap[VIRT_FLASH].base;
+    int64_t realsize;
+    BlockBackend *blk;

-    virt_flash_map1(vms->flash[0], flashbase, flashsize,
+    realsize = flashsize;
+    blk = pflash_cfi01_get_blk(vms->flash[0]);
+    if (blk) {
+        realsize = blk_getlength(blk);
+        realsize = realsize < flashsize ? realsize : flashsize;
+    }

Stefan recently posted "nvdimm: read-only file support" which
might be a better way to achieve what you want:
https://www.mail-archive.com/qemu-devel@nongnu.org/msg741137.html


Flash0 is read-only and shared by all VMs, but Flash1 is not and private for each VM.

Btw., how to create a nvdimm device mapping to address range 0~128MB?

+
+    virt_flash_map1(vms->flash[0], flashbase, realsize,
                    secure_sysmem);
-    virt_flash_map1(vms->flash[1], flashbase + flashsize, flashsize,
+
+    realsize = flashsize;
+    blk = pflash_cfi01_get_blk(vms->flash[1]);
+    if (blk) {
+        realsize = blk_getlength(blk);
+        realsize = realsize < flashsize ? realsize : flashsize;
+    }
+
+    virt_flash_map1(vms->flash[1], flashbase + flashsize, realsize,
                    sysmem);
}

--
2.23.0


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