On 16.03.2017 10:51, 李强 wrote: > Hello Gerd, > >> -----Original Message----- >> From: Qemu-devel >> [mailto:qemu-devel-bounces+liqiang6-s=360...@nongnu.org] On Behalf Of >> Gerd Hoffmann >> Sent: Thursday, March 16, 2017 5:31 PM >> To: qemu-devel@nongnu.org >> Cc: Gerd Hoffmann >> Subject: [Qemu-devel] [PULL for-2.9 4/7] cirrus: add option to disable >> blitter >> >> Ok, we have this beast in the cirrus code which is not used at all by modern >> guests, except when you try to find security holes in qemu. So, add an >> option >> to disable blitter altogether. Guests released within the last ten years >> should >> not show any rendering issues if you turn off blitter support. >> >> There are no known bugs in the cirrus blitter code. But in the past we >> hoped a >> few times already that we've finally nailed the last issue. So having some >> easy >> way to mitigate in case yet another blitter issue shows up certainly makes me >> sleep a bit better at night. >> >> For completeness: The by far better way to mitigate is to switch away from >> cirrus and use stdvga instead. Or something more modern like virtio-vga in >> case your guest has support for it. >> >> Signed-off-by: Gerd Hoffmann <kra...@redhat.com> >> Message-id: 1489494540-15745-1-git-send-email-kra...@redhat.com >> --- >> hw/display/cirrus_vga.c | 9 +++++++++ >> 1 file changed, 9 insertions(+) >> >> diff --git a/hw/display/cirrus_vga.c b/hw/display/cirrus_vga.c index >> 6ffe64f..326d511 100644 >> --- a/hw/display/cirrus_vga.c >> +++ b/hw/display/cirrus_vga.c >> @@ -205,6 +205,7 @@ typedef struct CirrusVGAState { >> uint32_t cirrus_bank_base[2]; >> uint32_t cirrus_bank_limit[2]; >> uint8_t cirrus_hidden_palette[48]; >> + bool enable_blitter; >> int cirrus_blt_pixelwidth; >> int cirrus_blt_width; >> int cirrus_blt_height; >> @@ -960,6 +961,10 @@ static void cirrus_bitblt_start(CirrusVGAState * s) { >> uint8_t blt_rop; >> >> + if (!s->enable_blitter) { >> + goto bitblt_ignore; >> + } >> + >> s->vga.gr[0x31] |= CIRRUS_BLT_BUSY; >> >> s->cirrus_blt_width = (s->vga.gr[0x20] | (s->vga.gr[0x21] << 8)) + 1; @@ >> -3024,6 +3029,8 @@ static void isa_cirrus_vga_realizefn(DeviceState *dev, >> Error **errp) static Property isa_cirrus_vga_properties[] = { >> DEFINE_PROP_UINT32("vgamem_mb", struct ISACirrusVGAState, >> cirrus_vga.vga.vram_size_mb, 4), >> + DEFINE_PROP_BOOL("blitter", struct ISACirrusVGAState, >> + cirrus_vga.enable_blitter, true), >> DEFINE_PROP_END_OF_LIST(), >> }; >> >> @@ -3093,6 +3100,8 @@ static void pci_cirrus_vga_realize(PCIDevice *dev, >> Error **errp) static Property pci_vga_cirrus_properties[] = { >> DEFINE_PROP_UINT32("vgamem_mb", struct PCICirrusVGAState, >> cirrus_vga.vga.vram_size_mb, 4), >> + DEFINE_PROP_BOOL("blitter", struct PCICirrusVGAState, >> + cirrus_vga.enable_blitter, true), > > The default is 'ENABLE'? I think there should be 'false'.
I think it has to be enabled at least for the older machine types - otherwise you change the hardware of guests during migration. Thomas
